How is aatrox broken?

I see people saying the new aatrox is broken but how? I see him lose to rivens without having a chance.

Riven has mobility, damage, an execute, shields, and doesn't even need any skill to hit her q's.

I still don't see how people think he is broken when he has damage but he isn't going anywhere,no shields,if he doesn't hit the q at the end mark aatrox is a total garbage champ. Once he goes in He is in there is no stun then Q'ing out of there like riven.

So I ask how is he broken?Because riven can make him useless.And if aatrox is broken shouldn't riven be more broken?