If a champion is versatile, isn't that a good thing? I'd really hate it if a champion was ONLY meant for one position, or nerfed to be shoe-horned into that position... I personally thing Yasuo being playable in other lanes is a good thing, just how I like it when other champions can too. Like Jhin can go mid or ADC, Maokai can go jungle, top, and support. Malphite can go top, mid, jungle, and support. And so on. Yasuo being able to strive in other lanes isn't a bad thing and never should be seen as bad for any champion imo.
Also, other champions have just as much synergy. Riven is built around AA resets, Malph also has an AA reset as do other champions. Yasuo isn't the only one who abuses Fervor just so you know ;P I'll agree Fervor is currently the most used/abused keystone, but that's because it works on literally every AA or AD champion. Gnar is a heavy user of Fervor, as is almost every ADC. To pin all the blame on Yasuo really isn't fair considering it isn't his fault, the keystone itself is too strong. I only would have agreed if Fervor was only good on Yasuo to abuse, but that isn't the case really. It just works really well for him, as it does for other AA/AD champions.
I think his well-roundedness is good though. We should really expect champions to be well-rounded, and not forced into one role or only one build path/play style. It's why I like playing flexible champions, though I myself dont play Yasuo. I could never get good with him and that's okay. I still consider him a good champion, but not broken or OP like everyone else thinks. He's easy to counter because his weaknesses are pretty obvious. Not to mention one of his biggest champion counters is a very easy champion to learn (Annie).
Also, for your last bit, I think Ekko is a good example. He was meant to be a bursty melee mage, but ended up doing better as a tank/bruiser build instead. And if you want older examples there was AP Nasus, AD/AS Lulu, and AP Yi. Even Blue-Kong used to be major issues too when they clearly weren't intended. There are plenty of examples of this, the difference is whether or not that unintended build has any clear weaknesses/counters.
I do agree tank yasuo was an issue, but Riot balanced that by restricting the armor pen to crits only. So now Yasuo has to prioritize crit more instead of building PD + tank items. Crit Yasuo is fine and pretty healthy. Has clear intended weaknesses and his abilities are still easy to deal with and dodge (CC will always rekt a Yasuo at any point in the game, so someone like Annie or Naut are perfect counters to him).
I would like to hear your thoughts on why you think a champion being versatile is bad though. That point really struck my curiosity :)
has the most stats out of any zeal item, while being cheaper. It doesn't have the damage boost of RFC or Shiv, but the PD speed makes up for it when kiting or chasing. If it stopped here, it would be fine. But nope. 12% damage reduction, on an item intended for squishies.
are just a few of the many, many champions that can put an equal-skill level Yas in the dirt very, very easily.
this particular game, there's always 
.
. I'm not sure how he is only good top though. I don't play as much anymore so keeping up with the meta/trend is not really something I have down.
