Honestly, the only characters that have no room for growth whatsoever are Iron Fist and Ryu. Now, I’m not saying they are bottom 2, but they do contribute so little and have so little that they will never, ever make top 20. Maybe some secret tech can come out and suddenly make Hsien-Ko or Wright god-tier, because this is Marvel. However, Ryu and Iron Fist really have no fancy tools going for them; they just suck.
Only characters worth banning are those that invalidate the lower half of the cast. Pretty much, you need to ban Vergil, Magneto, Viper, Wolverine, Zero, Firebrand, Spencer, Morrigan, and Taskmaster. I’ll even accept characters like Dante and Nova because I can see them having trouble against certain low tiers, but the others I mentioned can invalidate a fair amount of the cast.