-Ult auto-hits off of other ults, holds people helpless in the air, and reduces armor while leaving him in perfect position to follow-up before any of the victims can react
No other ult in the game requires an opponent to be subjugated to a particular type of CC to even cast.
They tend to just be available to cast when they're off CD.
Relying on allies to set up his ult is a con.
It's also worth pointing out Yasou can just as easily be placed in a bad spot from his ultimate, and he's not un-targetable mid-ult and can indeed be killed while performing it, which can result in plenty of damage for him.
-Doubles his crit rate
And lowers his total damage on a crit to 90%.
Double crit is also way less powerful than it sounds.
When AD Annie is at 150% DPS Yasou is at 180%, with IE it's 175% vs. 225%.
So double crit is only difference of 20% or 29% total DPS.
Vs. someone with no AA steroids at all.
It's worth pointing out most tanks, fighters, assassins, marksman, and supports have some kind of AA steroid or on-hit effect that prevents Yasou from doing 29% more DPS than them with the same items.
And yes, I did say supports. Janna has a +50 AD steroid, Taric a +70 AD steroid, Alistar a +90 AD steroid.
I don't really see how doing 29% more DPS than AD Annie is particularly impressive.
I really don't see how Janna out-DPSing Yasou for the better part of a game is either, or AD adventures Taric: and Taric has an armor reduction steroid his entire team can benefit from as well.
-Has a free "Fk you" to any projectile in the game
Most light fighters have something like that. Jax does that to auto-attacks, Kayle to damage, Fizz to skillshots, Nocturne and Fiora to spells, Wukong to lots of things, Tryndamere and Aatrox to dying, Poppy to everything.
-Has a shield even if he can't wall off your projectile
His shield is mostly only useful in a poke-war, in a burst war or vs. anything melee range it's fairly flimsy.
Between his ult's armor down debuff, Wind Wall, and auto-shield, something's GOT to give. Paired with champs like Wu and Malphite and there's literally no way I can see an opposing team winning a team fight against him.
Without Yasou in the picture at all: you deserve to loose a team fight is a Malphite pulls off a beautiful initiation that sends your entire team flying within range of some heavy-hitting fallow up.
Winning team fights is more about placing yourself in a situation where the enemy Malphite doesn't get to do that and yours does.
You can't REALLY run from all that, and to boot he cuts your armor in half AND auto-crits you with his doubled crit rate. Is it me or could this champ be looked into?
First - he penetrates 50% of your bonus armor, which is actually a pretty massive difference then 50% total armor.
Second - only Yasou gets the 50% bonus armor penetration, he doesn't debuff your armor (IE reduce it). It's still at 100% strength for everything else nearby.
Which is also a pretty important distinction to make.
Third - most light fighters and medium range marksman have 2 AA steroids.
Consider Vayne has +70 AD and 20+2.66% max HP per hit in true damage (~70 per-hit vs. a 2k HP target, or the physical equivalent of ~122 vs. the 75 base armor (42% DR) most squishies have @18).
It's worth noting here that for Yasou's double-crit passive to out-DPS both of Vayne's AA steroids vs. a squish, he'd need over 700 total AD.
Within an average game length, his typical build, bases, and 10 bonus points for runes/masteries will only take him to ~240.
Edit: If it IS me, no need to be nasty, but any advice would be lovely.
Yasou's mostly a case of smells OP, looks OP, sounds OP, but is objectively and mathematically pretty balanced.
Mostly what he does have going for him is a good set of tools to deal with a lot of situations so he doesn't fall into scissors vs. rock traps - which makes dealing with him fairly nuanced as there's no obvious weakness you can easily exploit in most situations vs. him.
If a fighter like this gets their hands on him he is toast. And not to mention his base health is garbage.
or 
Well that is just how it works. But he is a very easy gank when extended. He needs a great knock up on your squishies to be called over powered because otherwise bruisers spread his ass open wide. Any sort of hard engage that he cant wind wall means death. If he isn't fed when the first team fights start happening you have to catch him and focus him before he gets a knock up. And once a Yasuo starts feeding it is near impossible for him to be useful and come back.
''Dont you dare leave me out!''
into 
. Come at me bitches.