In regards to the whole Cloud discussion, I can see where the complaints come from. Much like Mario, he's deemed too good for how easy he is to pick up and play, especially when you consider that there are much harder characters to use that aren't even worth it like Peach and Shulk. Cloud gets more flack for being 'pay to win' and generally being considered better than Mario. He also does far better against lower tiered characters than Mario.
That being said, every character takes some actual thought and skill to be good with. M2K and Tweek aren't just pressing buttons when they play. I myself constantly fear 2 things with Cloud: getting gimped and wasting my limit.
As for Mewtwo, I've said it before and I'll say it again, I'd rather a nerf, be it to nair, disable or footstools. Because **** infinites. Aaaand Mewtwo has been top tier since his debut...in Pokemon. And he's been considered at least high tier in Sm4sh, usually moreso top tier ever since Abadango won Pound.