The reason we are not running pure
Toxin vs corpus health
pure Corrosive vs grineer's armor
Viral versus Infested
Is the convoluted and contradictive evolution of defensive abilities of the ascertained faction's high tier units directly countering your primary elements combinations on your weapons!! Look at the bonus damage and damage debuffs when using certain elements against the same faction! https://warframe.fandom.com/wiki/Damage#All_
Now take a good look at Corpus health types specifically because I think that is the most gnarly faction with all their "special exceptions" that most general average person would just feel 'oddly unsatisfied shooting at'
Health types:
Flesh: Consists of all Corpus humanoids including bosses like The Sergeant and Alad V. Also includes Drahks, Hyekkas, the Stalker and the Tomb Protector.
Shield: Is possessed by all regular Corpus units, Regulators, Grineer bosses and Corrupted Vor. Is not possessed by Locust Drone.
Proto Shield: Possessed by every Corpus boss (including Zanuka), Nullifier Crewman, Corpus Tech, Sniper Crewman and the Stalker.
Ferrite Armor: Possessed by Corvette, Frigate, Carrier (Enemy), Gox, Locust Drone, Humanoid Corpus bosses and Oxium Ospreys.
Alloy Armor: Possessed by Bursas, Corpus Robotic bosses.
Robotic: Refers to all Corpus robotics including robotic bosses like Ambulas and Zanuka. Is not possessed by Locust Drone.
Now take a look at a small section in the wiki that shows some exceptions against certain things you are shooting at!
Now this is the only things most of you would be unaware off so far! The faction bosses most of the time either completely negate status type damage or they reduce it and are not weak to it at all. Another thing is damage Bane mods such as Smite Grineer or Smite Corpus practically only negate the designated faction's debuffs to specific damage type and the damage debuffs for using the wrong element against a faction returns to normal levels aka average -30% damage reduction becomes 0% again meaning you deal the amount of damage you are meant to! Unless it's a Primed Faction Bane mod which basically double dips your damage as some people like to say but that is not true either it basically increases your damage past that 0% that is already debuffed because not only are you using the wrong damage type but also using the wrong elemental combination against this specific faction! Now why do I say that? Because Bosses and higher tier units are not affected by this damage type specifically namely wait for it... Viral and Slash! Ideally what everybody wants to use is this elemental combinations versus a a specific faction! Against Corpus that would be Toxin + Magnetic + Viral + Corrosive + Electric damage! Now why is that? Because corrosive 'Strips' the Ferrite and Alloy armored modifier from Robotic health! Which explains why people started to use 2x Corrosive Tau Shards in their Warframes because this reduces the total elements required to cover all your bases against a certain faction! This includes Infested AND Grineer as well!
PS: Taking a break will edit this post further later...
Edit: Against Grineer: the ideal elements would be kind of similar! Heat + Corrosive + Cold + Viral!!
This is outstandingly impossible to achieve vs Grineer because Heat and Cold combine into Blast create the only element in the game that is only useful versus rare infested and certain unarmored machinery which makes it horrendous choice for all Warframe content! This is weird dude why did you chose cold? Because it's increasing critical damage against health by 50% additively before mods!! Meaning it's similar to how incarnon adapters increase your critical multiplier by at least 2x or even 3x depending on weapon!! Why heat damage and not slash? Slash is good because it's the only damage in the game apart of "true damage" that completely bypasses armor and is otherwise weirdly referred in wiki as "cinematic damage" Now here comes a shocking revelation!!!! Slash damage feels 'oddly unsatisfied shooting at' is because actually it's bad versus Grineer because it has a minus modified against Ferrite armor and Alloy armor by -15% and up to -50% damage against Alloy armored enemies! Why would you ever use slash damage against armored units?? Now here comes the effects of Corrosive! Corrosive element works in a way where it reduces this damage reduction to your damage by % based on how many procs it has on armored target! From 10% per proc to 100% armor reduction at 10 stacks!! And 120% armor reduction with 2X Tau Corrosive shards on your Warframes making it possible to completely remove the armored modifier and make you deal 'true slash damage! So note that if you mod extra Corrosive with Tau Shards never use Radiation damage because it does not give you the bonus damage against armored units if all of its armor is removed! Same case as Slash the only reason Slash damage got popular was because a certain player before the elemental damage rework corrosive was not what it used to be today and this infamous Infested unit called Juggernaut and players were shocked at the fact that they could not kill this enemy no matter how much Corrosive or Heat or Gas they had build on their weapons because it had innate whopping 40% damage reduction including the elemental damage resistances it had in place!! More on that in infested enemies section!!!
Infested enemies: Slash + Viral + Cold + Heat now why Cold damage again man I can't believe the way you are playing with my emotions couldn't it be as simple as Slash Viral? Here is why Slash procs greatly benefit from Base damage and Critical Multipliers and this Cold proc delivers you this free multipllier so why the heck not!! Another thing is why Heat and not Corrosive again? Because before you stack Corrosive to max Viral+Slash is going to kill the infested monster before you even apply all that Viral and Corrosive and Heat believe it or not are anti synergistic the moment a heat proc appears on a armored enemy they lose -50 armor which makes corrosive procs reduce less Armor per proc meaning you reduce 5% armor up to 50% at 10 stacks!! Then why add Heat damage ? Are you kidding me? Did you even look at the table I have given you at the wiki or not? All infested health is weak to Heat damage including it's armored high tier units meaning it's the ultimate element against this faction! Guess what it has the same modifiers as Slash + to top it off it's better scalling linearly instead of exponentially and it's infinite scalling! Could you be talking about Gas damage and not Heat damage? Excuse me listen I am once again telling you to look at that wiki table and tell me how does Gas scale ? It doesn't 🤣 Digital Extremes has screwed us somebody call the person responsible we need to immediately call the extremists community to shut this situation down and protest and over react as hard as possible and give the developer a anxiety attack thinking that his game is going to die out from every player going on a Strike because they don't like this mechanic!!! Okay at the end of the day this <random> damage I shoot feels 'oddly unsatisfying while shooting at the enemy in this game' Why are high tier units resistant to the same damage type the weaker units of the same faction are to? Because if content in this game ever becomes too addictive and satisfying to the people they are going to play unhealthy amounts of hours and damage their health and have real life issues because once you are addicted to a game you are always addicted to a game until this day you are finished and satisfied with this game and it feels like you have completed everything you wanted to do and Reached the true endgame of reigning supreme in your air bending super powers!
Murmur faction: Electric + Radiation + Heat now Honorary element here is Cold and Gas elements because the slow in itself is useful against every faction the problem is "Cinematically" Cold damage is not supposed to be useful against Machinery and most of those mini mechanical units and nekramechs and even the Murmur enemies itself are quite immune to crowd control so making enemies displace or stack in close proximity is hard! The reason Heat is good is because Heat is surprisingly once again stacks very well and easily you just need a heat weapon and mod it with radiation courtesy of the new Radiation mods and you are set! Easy setup and nothing complicated. Electric damage on the other hand is simply amazing this patch not only does it work great in melee with Melee Influence Arcane. Procing electric status also makes most of the enemies that are Robotic have chance to hit and damage to the body parts of nearby enemies! Why is that useful you ask because Robotic enemies in Deimos require you to hit specific body parts in their body in order to destroy said body parts and make them explode making quick work of any nekramechs around!! And Murmur faction has similar mechanics to some of their enemies making Elements that are accompanied by AOE damage weapons like Heat beams,chains and Gas clouds made by Gas status and Electric Status chaining to body parts makes hitting these body parts easier! I know what you thinking now Equipping Ignis Wraith and modding it for Gas electric and Radiation and be like why am I lying to you all!!
I did not made this post to S#&$post or meme on your ignorance I made it because I wanted to show you that these elements's status effects are useful against these specific factions for actual use case scenario to have in your Primary weapon or secondary or Melee weapons elements! Meaning you can go ahead and use this on your Primer or damage setups when I say Heat and Cold I don't mean Blast element at all same thing about other examples I have given in a ideal hypothetical environment you can have all these elements in a single weapon not in a modding setup!!
Viral is great status effect it doesn't actually increase your damage it basically reduces the total amount of health the enemy has making you kill the enemy quicker it was a solution back before the Elemental Rework to remove the "Bullet Hose enemies" from the game!
My last edit: this is just to stick to the topic's main question!
Remember when I mentioned Gas does not scale well! Toxin does! The problem here is again ideally what you do with Toxin is combine it into Viral which is a huge waste because it's another wonderful stacking element similar to Heat the only problem here is it's got a limit of 10 stacks! Unlike Heat which stacks linearly infinitely, Toxin damage is kinda similar to Slash damage in a way it but it does not bypass armor it only bypasses Corpus Shields and it's damage does get reduced by armor BUT gets the same similar boost from critical multipliers! It's also stacking its individual toxin procs into one big stack of 10 toxin procs in 1 damage instance unlike Slash it acts more like Heat damage in this case it lasts 6 seconds living as a single 10 stacked Toxin proc all running out at once!! I don't think it gets boost from Base damage of the weapon or mod damage only elemental damage and faction mods and certain Warframe buffs Since I am sick of reading the wiki looking at formulas I will just say from my experience in-game from now! Basically Toxin damage works In a way where the more times you reapply the 10 stacks per status proc the more damage you end up doing!! It is also very important to have as much big Toxin proc while applying the stacks up to 10 stacks as possible meaning it varies based on "how high damage numbers the individual damage procs all the way up to 10 and their Sum is your resulted DPS meaning your total burst damage is capped but your DPS is not as long as you keep refreshing the toxin proc u will deal the accumulated 10 stacks damage! This makes it good with fast attacking weapons and hybrid weapons with both good crit chance and good status chance ideally more leaning towards Status chance because reapplication results in more DPS the most most proper way to use this would be either to use both stealth multiplier and a finisher attack to stack as much burst as possible on your initial burst flourish and sum up a big proc Or use ground finisher to boost the procs damage by like 1000% about 10 times to make one big 10 000 damage toxin proc! The problem is most ground finishers on stances force proc slash and not Toxin and it seems to be not a normal slash proc...The last way to use Toxin procs would be with a specialized Riven with -status duration which means you use high multishot with very high status weapon 200+ status chance +5 bullets or more means instantly procs 10 stacks and runs out and u roll the dice in 10 stacks again resulting in varied damage bursts of summed up Toxin damage.