If played right is a very difficult thing for aatrox, and you're also overexaggurating.
Aatrox's damage w/o any AD is actually pretty minimal, as the base damage on his Q is a fairly low 10 - 90 (12.5 - 112.5 on swing 2, 15 - 135 on swing 3) (amp'd by 50% if hitting the sweet spot), but the scaling is massive, thus leading most people to build an early Caulfields before starting their Black Cleaver.
Aatrox's Q might be "out damaging" if he is able to consistently hit all three sweet spots, but realistically, unless he picked into an extremely strong matchup or against a player who can't dodge his Q's, then his damage is going to be significantly weakened, as his early Q cooldown is 14 seconds. He has to hit three skillshots within skillshots at different ranges that all also lock him out of basic attacks during them, which is hugely punishing if he misses, thus the reward for hitting them is quite large. Think of it this way. Aatrox's Damage is entirely in an ability that is three parts, has a conditional damage boost, has a long cast time and a long cooldown, it's going to hit hard because thats where they want to allocate his damage, as his basic attacks w/o passive are quite weak due to his low base attack speed.
Riot tends to not really focus on entire classes w/ regards to balance, the only time in recent memory that they likely hit an entire class was with the Conqueror nerfs and perhaps the Runic Echoes buffs, otherwise they're pretty good about letting outlier cases be put down, See the nerfs to Rageblade/Vayne as nerfs to specific champions w/o affecting the larger ADC roster in most ways. Riot generally mostly just nerfs bruisers because of community outcry, when in actuality they're a fairly mediocre class in the high elo meta, it's the same reason that much of the ADC changes got reverted.
Side note. Q isn't an AOE crit, it's an AOE ability, but hitting the sweet spot causes the crit indicator to appear, as a way to show you did increased damage. Some abilities that also do this are Gragas' Q when charged, Karthus' Q vs. a single target and Sylas' W vs. a target below 40%. Just a bit of clarity, since critting is a different mechanic from doing boosted damage, tho you're correct about minion aggro.
Aatrox hasn't been nerfed as he was buffed in 9.9, before MSI and before the pro season started. And as his stats for soloq have started to settle to being "sub-50 for sub-plat, 51% for plat+" in terms of WR (u.gg as my source), then they were likely waiting for pro play to see what should be tackled regarding his kit, as his soloq performance wasn't showing anything too extreme. I suspect we'll see nerfs very soon, as he's been shown to be quite the presence in the few matches that have been played.
