I think you should take a look at the full changes.
Umbral Dash (E)
healing increased from 20/22.5/25/27.5/30% to 20/25/30/35/40%
Cooldown lowered from 9/8/7/6/5 to 7 at all ranks
They're nerfing his E's cooldown again, making it IMPOSSIBLE for him to do any form of reliable combo but greatly increasing his healing versus champions. Making it so in ult form, when he's going man mode on you, he is healing a significantly larger amount of HP and this also synergises with his item build picking up more HP and healing now.
World Ender (R)
160/140/120s Cooldown
"Aatrox reveals his true demonic form for 7/10/13s and begins to fill a Blood Well. The Blood Well stores all healing he takes during this time. At the end of the effect, or upon taking lethal damage, he heals depending on how full the Blood Well is.
During this time, The Darkin Blade has no cooldown and resets the cooldown of Umbral Dash. Additionally, Aatrox gains Movement Speed when not in combat with champions or turrets, 20/25/30% Total Attack Damage, and he fears nearby minions."
Looking at these changes, there's quite a few things to note. First of all, the duration increases gradually as they want him to be fighting in ult form a lot more now. Secondly BOTH his Q and his E reset in ult form, making him reliably commit to doing massive amounts of damage as seen here.
https://www.reddit.com/r/AatroxMains/comments/b3xn25/demonstration_of_the_new_aatrox_ult_rework_on_the/
Finally, the issue about URF mode Aatrox is that he's going against other URF mode champions. Even if he's subpar in URF, these changes make him super overbearing during ultimate and makes him even more useless in base form. The problem with Nasus' and Vayne's ult buffs are that they didn't sacrifice anything for it, Aatrox is basically sacrificing his entire kit outside of ULT as he's relegated to being a poke bot with the E c/d nerf.