The reason why I hate yasuo:

Is because once he gets fed, it is impossible to effectively counter build him even during his so called "weak midgame". His ult halves the value of any armor you buy and building hp isn't too useful because of the amount of sustained damage he does. Building reduces his damage, but won't stop him from constantly chasing you with his ridiculous mobility and eventually killing you while you barely manage to dent his shield. Oh and if he lands a tornado on your backline they are donezo because of his burst of q+r+auto crit pretty much doing 80% to a squishy. The only champions that can stand up to him are duelists like fiora/trynd/yi who possess the problems as yasuo. As such if a yas gets fed, it takes at least 3-4 to stop him instead of 2 people for other champions like assassins/mages/tanks/some fighters.