What I would do to fix Aatrox
The issue as I see it is the fact his Q is clunky to use, his E is there to "fix" his Q's issues and his passive just feels like a showcase of a new mechanic, not proper execution of it. His ult feels like it has no purpose other than to make him look like the old Aatrox and that is it.
-His cooldowns early on are too long -the heal mechanic, and his ult feel shoehorned in -his Q has so many issues with it that make it extremely difficult to use effectively.
Ironically, only his W seems ok where it is, as it CC that works well and can be used to setup plays for you and your team. So with the grievances above I'm going to try addressing them in a way that would make Aatrox more fluid and more interesting to play.
His Q Darkin Blade would be castable while moving at all times, this would enable him to easily reposition to hit enemies at the optimal angle and would also have future synergy if for example an Aatrox player took
if they wanted to. This would also add counterplay against him, making slows an effective counter to a rampaging Aatrox.
His E Umbral Dash would would be replaced with a new E called Bloodfeast Bloodfeast would passively fill your Bloodwell from killing minions, as well as doing damage to large minions, monsters, and champions. When activated, Bloodfeast would would consume your total Bloodwell and cause Aatrox to ignore unit collision and gain bonus movement speed (based on the rank of Bloodfeast) for X seconds. Additionally, every-time you damage a Champion or Monster be healed for 60/70/80/90/100 (+3% of total health) health. The "X" amount of seconds would be determined by how many segments of Bloodwell where consumed (1 second for each segment with lets say each segment is worth 100 HP).
I know that Umbral Dash was meant to serve also as a gank tool for Jungle Aatrox but it has always felt tacked on, a bonus movement speed seems far better especially with the change of making his Q castable while moving a thing.
** Finally Aatrox's ultimate World Ender** would now be dive mechanic akin to Aatrox's old Q, would deal physical damage in an area, and apply a short knockup. Aatrox would gain the ability to revive from his Bloodwell, but his E Bloodfeast could still consume Bloodwell charges if he chose to. His Bloodwell would still generate over time as it currently is, but at a slower rate to account for his new E Bloodfeast.
This change is about giving Aatrox's ult some oomph to it and harkins back to the times of engaging with your Q on old Aatrox, it feels impactful and gives those wings a reason for existing.
These would be my changes to him, this is about making him effective but also feel good to play. I didn't really post numbers here because I'm not sure what kind of tuning he'll need, aside from his E's heals. The rework feels slow and maybe that is intended with the Claymore but right now he feels like it slowing him down. I feel like his heal shouldn't be an always on thing which is why I made it an active thing tied to an ability he has to build up resources for. Yes people will build lifesteal eventually but early on this will make laning against him less frustrating.
don't have anything to compare with his mobility, even if he's not the fastest in the west.