The problem with buffing Yasuo is his multiple multiplicative damage. Every amount of small damage gets multiplied multiple times to create big damage when he gets items. That's why with just IE and a completed zeal item, he can output massive amounts of damage no matter how much you crushed him in the early game.
I agree he probly needs buffs, but you can't do that until you rework his ridiculous kit. Instead of getting 2 different passives which are both better then the average passive, his bonus crit chance and crit damage penalty should be tied to levels of windwall so he has to level it up like Darius does with his E to get armor pen. I have no idea why they gave him 50% armor pen after hitting somebody with his ult considering how easy it is with teammates like Zac, Malphite, or countless others; that passive should just be gotten rid of alltogether. Once you do stuff like that, it becomes more fair to start buffing his base damages.