I personally believe that the core problem with Warframe, specifically with regard to the concepts of "difficulty" and "challenge," is the staggering disparity between starter level content and what is considered "end-game," and the fact that the players' power level relative to that of enemies is contained entirely within our gear. It's the reason why content like The Steel Path is annoyingly difficult for some, and still boringly easy for others.
Warframe's gameplay is set up to have very little skill factor. The game is at its heart a horde shooter. It is designed to allow the player to, with little effort, slice or blast their way through enemies in droves. Your effectiveness is not about how personally skillful you are (ex. your aim, your mastery of movement, your ability to out-think enemies). You can play the game that way, and sometimes I do, but because that is clearly not the expectation, doing so can dramatically increase the difficulty and makes the omni-present grind horrendously tedious. And then you turn around and see someone flying around at super-sonic speeds pulling a nuke out of their pocket every 5 seconds.
This is a situation that is impossible to balance. People who don't wish to play with the most optimized set-ups, and just want to play with what's fun for them are often (depending on what equipment in particular they are using) going to find higher level content to be frustrating and overly challenging. While players that do play with the most optimized set-ups, whether they find it fun or not, often feel the game is too boring and not challenging enough. It's the reason why anyone unironically saying "get gud" in regard to Warframe should be laughed right out of town, because in this game "get gud" actually means "change your load-out so you are even more over-powered than before."
Until this problem is solved, no one will ever be able to have a meaningful discussion about difficulty in Warframe. Different players will always have different tolerance levels for difficulty, and that's ok, but it does present a significant challenge to the developer when they are making a multiplayer shooter where everyone is on the same difficulty tier at all times. But on top of that, DE also has to contend with the fact that two players can be playing a dramatically different game based entirely on what weapons or Warframes they brought to the mission with them.
Contrast with classic Destiny. That was a game in which pretty much any strategy you used was viable. The various classes, subclasses, and weapon types varied not by power (barring some relatively minor balance issues), but by playstyle. And yet no matter what equipment you chose to use, the game was still fun, engaging, challenging, and intrinsically rewarding, because every playstyle basically existed at the same power level. Your ability to participate in and complete end-game content was determined by your character level (or light level later on), not by the weapon you equipped and which perks it rolled with. And yet, there was still room to min-max if you wanted to, but doing so didn't dramatically change the way the game was played. While end-game equipment did offer advantages, there was no way to load-out to basically lol your way through the entire game, all the while complaining that it's too easy.
In my opinion, all of the balance issues with Warframe stem from the fact that there is such an egregiously large gap between the power level that players start with in Warframe, and what they are capable of achieving if they really want to, because there are too many points in between where players can land just based on what numbers they had on their arsenal screen.
So first I think we have to decide what kind of game we want Warframe to be. It is a horde shooter after all. You cannot have a slow-paced tactical experience where you must outsmart your opponents when you are being shot by 50 enemies at a time who are continuously respawning on all sides of you. And at the same time, you cannot have a meaningfully challenging and rewarding experience when you are so heavily encouraged to spam massive AoE damage just to get through the mission as quick as possible because you've got to run it 150 more times because the drop rate on the reward you want is so stupidly low.
Secondly, the growing disparity in the power level of, not just particular weapons, but entire playstyles needs to be majorly decreased. I know DE has recently taken some steps to address this problem (changes to armor scaling, shield gating, enemy accuracy). But frankly what they've done so far is a drop in the bucket. Walking into a room and exploding instantly because one enemy put a slash proc on you because you didn't come in mindlessly flailing your infested zaw at mach 3 does not make for a fun experience. I just want people to remember, difficulty and challenge are not the same thing. There is already plenty of challenge in Warframe if you want it, but we as players have been trained by the game itself to avoid as much challenge as possible. And simply increasing the difficulty accomplishes nothing but increasing gear exclusivity, because players have shown that no matter what level you crank the enemies to, someone will find a way to make it as easy as possible.
So in short, yes, the maximum potential power of players needs a big nerf, but enemies absolutely need just as much of a nerf. The extremes need to be brought back much closer to the baseline, so that any semblance of balance can be achieved. I don't mean perfect dps balance between every weapon in the game, which is obviously unrealistic. A Lato will never compete with a Kuva Bramma, and that's fine. What I'm talking about is taking away the ways in which players have found to basically break the game to bypass all challenge, which then takes away the need for enemies that are designed to break our experience. It will upset some in the short term, sure, but they'll eventually realize that they can still have fun and fulfill a power fantasy and be challenged at the same time, once the game is better balanced. But until this occurs, you will always have a game that is adequately challenging for some, but oppressively difficult for others, or a game that is fun for some, but mind-numbingly boring for others. And there will never be a perfect point that will completely satisfy everyone. But if the range of power is narrower, it'll be much easier to decide where the sweet spot is.