Broken is a very general representation of these champions, but in case they haven't realized it yet when you combine an assassin with crit it never ends well. I honestly don't know why they put crit in this game at all, it's like they were looking to make it less balanced.
It's called CC and waveclear. If your team comp doesn't draft enough cc you lose. If you can't land your skillshots you lose too. They you don't have enough waveclear to deal with the side lanes when they split, you lose. They aren't broken but they can be if you don't have the teamcomp to deal with great splitpushing potential and high damage threats.
Yi still takes more skill than Yasuo though lol
Play them if they're so broken.
