The old Aatrox was a lazy copout, and here's the simple truth why

His passive was just a generic revival like Anivia His Q was a less reliable Xin E, despite the small AoE, having less range and not being targeted His W was also a less reliable Xin W, because instead of both damage and healing you had to choose between them His E was an Anivia Q minus the stun and synergy hers has with her other abilities His ultimate was a Yi ultimate minus the movespeed and slow immunity.

Old Aatrox was far less unique than the new design, and the fact he was an amalgamation of weakened versions of other champion's abilities that didn't go together is exactly why he was never the best man for the job. Xin, Udyr, Yi, Jax, Vi, and Shyvanna could all always do better than him at his intended purpose.

The only time he's ever performed well is right this very moment, thanks to the removal of his W cost combined with Conqueror-- which they'll either nerf or buff other runes to match its strength.

It's purely coincidental that his rework timed just right with an overpowered rune making him finally a decent pick, since the team in charge of champion reworks isn't the same team that deals with runes. If they had held off the release a month or two, or been ready a month earlier then it would've been right when Aatrox was garbage again.