affinity glitch?

[ShinyShaymin]

While I am certainly not complaining... I'm running onslaught with my brother and our weapons aren't levelling at the same rate. We both have affinity booster from the twitch promo thing, but I'm earning nigh on 10x the affinity he's getting. The only thing I can figure is that I have the other 2 boosters going also, thanks to the sortie and the other part of the twitch promo. Is this a bug, or is trinity the affinity favored frame? 
To give you an idea of how fast it's going... I can level a weapon from 0 to 30 by the end of zone 2. 

Edited January 20, 2019 by 55141

[AXCrusnik]

Affinity is shared between the weapons you have a equipped. If you are using just Trin an a primary for example, while your brother has a full set of weapons, your primary will level a lot faster than your brothers.

Detailed affinity gain mechanics from the wiki:

Warframes and weapons gain Affinity for several types of actions, detailed below. Unless specified otherwise, all Affinity gained uses the split according to the general rule: 25% of the amount goes to your Warframe and 75% of the amount is divided evenly among all equipped weapons (25% each for three, 37.5% each for two, or the full 75% if only one is equipped).

• Kill an enemy with a Warframe ability. All of the Affinity goes to the Warframe.
• Kill an enemy with a weapon. Half of the Affinity goes to the Warframe and half to the killing weapon.
• Be near an allied Tenno when they kill an enemy. When within 50 meters of an ally when they kill an enemy, you gain the same total Affinity, distributed according to the general rule specified above. This doesn't reduce the Affinity gained by the killing player, and doesn't reduce the Affinity gained by other nearby allies. This applies to Archwing mode with much larger ranges for shared affinity.
• No weapons equipped. All of the Affinity goes to the Warframe.
  • This applies when the only equipped weapons are overridden by ability-created ones. (E.g. Using Exalted Blade while only having a melee weapon equipped.)

Edited January 20, 2019 by AXCrusnik

[Andvarja]

What frame is he running?  You're running a frame which doesn't really earn a ton of affinity through killing enemies with its abilities.  If he's running one which kills primarily through its frame abilities rather than its weaponry (such as Saryn), you can see this sort of disparity.
 

As you can see by what AxCrusnik posted, kills by the frame belong to the frame alone for the player.  It does not share affinity with the player's weapons.  However, those kills are still shared with the party and get the standard 25% to frame and 75% split among the weapons for party members.  So if you're running Trin, but he's running a Saryn or something, he's scoring a lot of your team's overall kills, and he's scoring those kills with his frame, and none of that exp goes to his weapons.  But those kills by his frame, so long as you're in range of him do go to your weapons (and frame, but you get my point).

Your weapon kills do the same 25%/75% split to his frame/weapons for him, but you may simply be doing less of the killing as would be expected in a Trinity/DPS pairing, especially if you're leveling a primary weapon rather than bringing a fully leveled and formaed monster.

The same goes for weapons to some extent, btw.  Weapons don't share affinity directly with other weapons.  So if he's using a Saryn and an Ignis Wraith to score the kills, while trying to level a secondary weapon he's never killing with, it won't earn much since it's mostly just getting things like the mission mini-challenge (score 30 kills, etc) and any kills you yourself may be scoring.

Edited January 20, 2019 by Andvarja