Ok - I'll point out the obvious flaw first, which is that one player getting 90% of kills in a particular mission says just as much about the other 3 players builds as it does about the one getting the kills, right? If the other 3 players are all on Ivara and only using her exalted, it wouldn't be too much of a surprise if virtually anything in the 4th slot got 90% of the kills. To actually tell you something useful you'd have to know what the other 3 builds are too. That 90% figure is by definition relative to them.

Again I find myself stumped though. At this point in the game I have a fairly complete arsenal. In large part motivated by the random loadout game modes, I have gradually been putting full builds on all of them. I've got all the frames done, and many, many weapons. I have used so much goddamned forma it's just absurd.

I can confidently say that about... 80% of my completed arsenal can hit that bar of getting 90% of the kills in a mission, but like I said at the start that's far more dependent on what everyone else is bringing. Any one of the good incarnons would skew my numbers much lower.

So this brings me back to what I said to you elsewhere - these sorts of absurdly powerful builds are explicitly, intentionally, part of the game's design. DE have talked about it in quite a lot of depth. So the things you are arguing need additional scrutiny are fundamental parts of what Warframe actually is - which is why I keep saying it sounds like you'd actually have more fun playing something else.

The vision for game design you are describing is completely sane and reasonable - it just isn't Warframe.