Unpopular opinion: Aatrox is actually pretty good.
Especially with the new fervor, Aatrox has decent clear, can solo drag at level 4, can gank pretty well, and is a great counter-jungler and amazing counter-ganker.
Of course, I'm talking from a jungle standpoint. Like Warwick, he has a weaker early game, but after he gets some attack speed he can get going. His ultimate is a great way to generate aggro from enemies, and you're basically a second carry if you play him right. If the enemy ADC gets Executioner's Calling, better reason to dive them in fights. And you can just build tanky to be even harder to kill than usual.
With the new BoRK buffs coming up, he's going to be even stronger. I won't be surprised if he becomes a popular jungler.
What makes him so bad?
as a support and he's actually pretty good. I agree with you on the fact that he's much better late game. However, his Q gives him a lot of sustain and makes trading work to your advantage because of his heal. His Q also makes it less detrimental to block skillshots in order to protect the ADC because he can easily recover the health from minions or enemy champions. The only thing I think isn't so good is how much mana he uses.