Look at fighters and other top laners
Olaf--free resistances passively from ult, all the time, while ult is inactive.
Nasus--bonus resistances and health with ult
Tryndamere--invincibility, while still being able to attack
Pantheon--gets to block unlimited damage for free just by using abilities.
Riven--gets a shield that scales off of AD
Jax--can block incoming damage and also gets bonus armor that scales off AD when he ults, plus bonus magic resist.
Fiora--gets a free spell shield
You see the problem? Aatrox has nothing like that except a shitty passive which should read, upon dying, sit there and die again in a few seconds.
He has no functional defensive abilities, and nothing to counter other champions directly.
Literally every other top laner and nearly every other champion, has some build in defense or shield. He has nothing. NOTHING. And his sustain is built into his auto attacks dependent on attack speed, which he will have no bonus when reviving from his passive.
A possible solution:
Passive--Bloodwell increases resistances as it fills up, alone with attack speed. Drains slower than currently set at, Revive only available when dying with a full bloodwell.
Also, abilities no longer cost percent of health, but set amounts, so as not to punish Aatrox for building HP.
There, I just fixed Aatrox. Hes fine now.