I think the fuclum of his problems is... guess what? the crit passive.
I liked that it doubled the crit chance but, weirdly enough, that it kept the same damage. Making items more stat-valuable is not a good sign of champion design to me ( i think the same about vlad and ryze ) because it forces the player to pick the same items because in the champion' s hands get broken.
Like broken-inducing design. wat.
They should have kept the double passive crit but halved the crit bonus - the reason behind this is that it made the long-term dps still at the same number as other champions ( or more due to other effects ) but made it more reliable with less items, so Yasuo could focus on other items... or totally skew it and adopt other choices not crit-reliant; in few words, the crit-portion of the passive would be more about "having the possibility of adopt side strategies more effectively" or "having a more pronounced but not skyrocketing damage spike" rather than "get crit and get broken", allowing more power budget on the other utility or offensive side of his kit. Hell, he could even become the adcarry/support everyone always asked.
So instead he got heavy sparse nerfs. Now i don' t know if he got better or the people actually picked him up again and realized how he is still powerful, but this core design problem remains. A problem that is not terminal of his own, for sure there is a way to have passives that increase stat values and still being healty, but that is to be seen already.