well yasuos real weakness doesnt lie in lane tho.
his real weakness is that he is a melee champion without an unconditional/long range gapcloser and no instant cc so his ability to just jump onto a squishy and instagib him is very limited even when he is fed.
he somewhat relies on his teammates to do the job. a khazix for example doesnt have this weakness and he is way more mobile, thats why khazix is a much stronger champion overall but his laning is weaker due to the mana restriction while yasuo has a free shield, a free dash and a free windwall all combined with a free medium-range farm ability in his Q, AoE damage from his EQ and an excellent buildpath.
yasuo has infact one of the best laningphases of all melee champions in the midlane because of how good his kit is for that.
now his OTHER important weakness (that is actually the reason people cry about him but dont understand why) is that he is neither a real assassin nor a real bruiser. he doesnt INSTAGIB with no chance to even flash like khazix/riven do and he also doesnt duel nearly as good as strong duelist champions like shyvana, garen, master yi, irelia and many others do. even if he is fed, basically a 3 item garen will kill a 5 item (those item numbers not including boots) yasuo no problem.
this is his main weakness. he doesnt scale good against strong fighters, thats how you can beat him on the map and not let him ever use his strong destructive ultimate.
also, always keep in mind what the enemy team gives up for having a yasuo on the team. sure if you have a zed against yasuo matchup, you give up the same thing but if you have an anivia, viktor, karthus or azir or even velkoz, you have a long range super high damage AP threat that yasuo cant deal with ever without his team, so they are somewhat forced to malph-ult-flash-alistar-something engage on your team and if you do not let that happen or they dont even have the champions for that and you force them to play the map against your team, yasuo is very very very much weaker than he appears.
a good example is actually the C9 vs FNC game where darius got a pentakill.
basically in that game, FNC had very nice aoe knockup engages with alistar, orianna and gragas and they have a nice way of getting that engage of with sivirs ultimate. so overall, a very strong composition around yasuo.
but they played against tristana, azir, morgana and lee (darius being more on the useless side here) who are extremely strong at a long range which FNCs team does not have. this FORCES fnatic to engage on them or they will lose slowly but surely.
now with the amount of peel and disengage C9 brings (morganas everything, tristanas ult/jump, azirs ult, lee sins fucking ult, darius slowing and possibly hooking enemies off his carries which he never even attempted) the engage doesnt just have to be good, it has to be perfect.
if you make one mistake or dont go all-in enough or hesitate half a second, you will instantly get shattered by their disengages and destroyed by their long range. you CAN win but you have to play better than them and they CAN win but they have to play better than you, which makes the game very nice and balanced.
this is how yasuo works but because i say hes more on the weak side is because he cant force his play onto you, he has to wait until you step out of line and then kill you while super strong mages like viktor can force everything onto you but then has to be careful not to step out of line himself.
basically you can simplify it by saying yasuo aswell as riven and other assassin-ish types rely completely on their cheesing potential and if you play perfect, they have 0% winrate. tho nobody plays perfect, its pretty balanced.