Not really that strong seeing how sensible to CC his Q is, try to CC a malphite or Vi, those are strong initiators.
My only problem with him is that he has to sacrifice survivability for any action he takes, want damage?
Pay.
Want CC?
Pay.
Meanwhile champs like Riven have no downside.
Heck even AP Xin Zhao is a better Aatrox if you want a sustain tank.
Aatrox's damage lies in his early, when his passive is up and he can go ham since he won't die, all the Aatrox i've seen rush BotRK than full tank, they also seem to love thornmail to duel adc better.
No need to hide it, lategame there are 100% many other better bruisers, that tank better, and deal more damage.
He's a very good splitpusher though, in duels he's quite strong.
It's sad that his teamfight potential isn't how his lore says he should be.
To the OP:
Ever tried splitpushing if you can't teamfight (Might not be your fault, it's just that certain teamcomp have always the edge over yours and you should totally avoid 5v5 fights.).
As i mentioned before he's a very good splitpusher, he does fairly well in duels and you can buy alot of time for your team to push somewhere else if you say you even buy GA, with your passive it takes a while to take you down.
We got even a new item to kill towers faster, remember that winions are the most OP thing when it comes to end a game where you don't want to Ace>Nexus.