K. I'd appreciate it if you would learn to use the enter key.
It's much easier to read lines than it is to read a wall.
Also, it is easier to extract meaning from this wall if you make coherent points instead of just rattling off random sentences about Yasuo.
Anyways...
Yasuo gets double crit to prevent him from building Tank. If he could build like Irelia but still be effective, you can bet your ass he would (remember when you could build Sunfire and Iceborne on assassins to become a god? Tank Yasuo would be worse than that).
Yasuo gets armor penetration because his items are pretty well defined. He needs two crit items (usually IE and a Zeal item of the week) and boots. Seeing as he is a melee carry and is VERY squishy, a GA is a must. This leaves Yasuo with two item slots that he can really work with.
He needs to get a lot of flat AD out of these, since all the crit in the world doesn't mean shit if Yasuo is hitting people with a wet noodle. He also needs lifesteal, obviously. So, one of his items will have to be a BT, Scimitar, or Maw.
If his LAST inventory slot always had to give him armor pen, his build path would have zero variation. Because he has armor pen innately, he is free to use that last slot for a situational item (currently, Frozen Mallet is most popular).
Yasuo IS Feast or Famine, but that's not really a problem. He is a hyper carry who is either an unstoppable god of death riding on wind, or he is a b5 12 year old named x_X_EDGELORD99_X_x trying to get clips for his montage.
He is hard to deal with when ahead, and pretty bad when behind. This is fine. When he is feasting, a good Yasuo can carry his team to victory. The famine, however, is the good part. At any point, a game can go irredeemably bad for a Yasuo. If Yasuo falls behind and doesn't get back online FAST, it's all over for him. So, this is most of his counterplay; take advantage of his 0 defensive mobility and squishy nature and brutally kill him over and over again in the early game.
As for windwall being annoying... yeah. It is.
So is Teemo.
The thing is, look at what Windwall does. It gives Yasuo 4 seconds of relative safety on a cool down of 24-18 seconds. For a champion that doesn't build CDR, that is huge. To give you an Idea of how long this is, if Yasuo burns windwall in mid, a support can roam all the way from bot lane to gank, and he will STILL have a pretty good window to kill Yasuo before windwall is up again.