Just make Yasuo a late-game champion.
This is my response to all those Yasuo threads I keep seeing recently. No, I don't have any problems with the champion, never had, and hope I never will.
Now, I could understand why some people would, though, so here is my suggestion to make him more balanced.
He has a critical strike damage reduction in his passive. How about we make it scaling? 30% at levels 1-5, 25% at 6-10, 20% at 11-13, 15% at 14-16 and 10% at levels 17 and 18. This way, he doesn't get insane powerspikes by just building a Phantom Dancer and critting his face off. It makes it so that he builds something else early on to not get hit by the crit damage reduction, and allowing room for other champions to get a jump on him. He can still build PD first, but that would make him kinda weak, seeing how he would have a 20 - 25% damage reduction at first.
Maybe this pushes Yasuo to build raw AD first by means of BF sword and a Pickaxe, maybe get a BorK first, and after level 11 he can start banking on some crit.