Aatrox Main here.
Aatrox's healing comes from three places, if he goes deaths dances first (which isn't usually the case, since its an expensive item that provides an inconsistent defensive effect, but I assume this is what happened to you. Usually this is only built first if hes doing insanely well)
- His E passive causes 20-30% of all damage (except for DoT effects) that he deals to champions to be returned as health. This healing is calculated POST armor and damage mitigation, meaning the squishier you are the more he will heal off this effect.
- His passive causes the 5-12% max health physical damage bonus to be returned to him as health. This is (to my knowledge) also based on damage post mitigation. Meaning that again, armor will reduce this damage, since it is physical. Building health will increase the healing from this effect, since it effectively increases the damage it deals. Worth noting as well, that his E passive activates on his passive's bonus damage, so if he's hitting an enemy champion with the passive auto attack, it'll heal for a little bit more than the damage it deals.
- Deaths Dance healing him for damage he deals to all sources by 15%, reduced to 5% on his Q, since its an AOE effect.
Finally, while under the effects of his ultimate, he gains 40 - 70% increased healing from all sources. This would effectively amplify the healing of Death's Dance, his E passive and his Passive.
This healing is a lot to look at at first, but it's also important to understand how Aatrox does his damage. Unlike a champion like Riven or Jax, Aatrox's damage is pretty much all allocated onto his abilities and his passive empowered auto. His auto attacks outside of that have an intentionally clunky and slow "wind down" period, which hampers your ability to do dps with auto attacks, and effectively makes them pretty worthless unless you're so ahead of your opponent that it doesnt matter. To put it in other words, you can't kill shit unless you hit your Q.
Aatrox's Q has a fairly beefy cooldown early on. It starts at 14 and goes down to 6 seconds over levels 3 - 9, as he ranks it up (worth noting that with the way Aatrox's Q's cooldown works, if he doesn't use all three Qs, then around 2~ seconds of the ability's cooldown are refunded per Q he didnt use. Thats the only way I can really explain it, its a little more complicated than that, but we'll just go with that as a rough estimate). The ability's base damage is also incredibly low, relative to other skills that you could compare it to, with it's base damage being only 10 - 90, before taking the AD ratio into account.
Aatrox's Q also has several things that increase it's damage. First, hitting with the edge of the blade (indicated by the more highlighted portion of the skill), increases the Q's damage by 50% and knocks the target into the air for 0.25 seconds. His second and third Qs also deal 25% and 50% more damage, respectively. With this all known, It's worth noting that, as an Aatrox player, my entire goal is to hit you with the 'sweet spot' of the Q, since the damage is pretty pitiful for how slow it is otherwise, but if i can hit those spots, the damage is fairly substancial.
With a Death's Dance in his pocket, Aatrox's Q will likely be hitting for around 200 to 350 damage, if he hits a sweetspot, or around 150 to 200 if he doesnt. These are pretty rough estimates. Roughly by this time, his full combo will probably deal around 600-700 damage if he manages to hit you perfectly (and honestly, this is much easier said than done). This is majorly reduced when he doesn't hit the sweetspots, to about 350 - 400 if we use the same math, which is pretty bad considering the cast times of the ability and the opportunity cost of using the skill, its pretty much never worth casting his Q if he cant hit the sweetspot, since simply auto attacking would probably do more DPS than the reduced damage of Q1 and Q2's non-sweetspot hits.
Thats where the insane healing you're witnessing comes from. Hitting multiple, squishy targets with his Sweet Spots, during his Ultimate. In this case, Honestly, if the opponent plays so poorly into him that they just let him land his entire combo on them, I'm totally cool with your team getting obliterated whilst my health bar doesnt move. Its that team's fault for engaging me in a way which benefits me so heavily. It's the same thing as "don't chase singed" or "stay behind minions vs. Blitz", if you play into it poorly then you're going to get punished, or if Aatrox plays the situation incredibly well, hes going to get rewarded.
With that in mind, Aatrox is a pretty difficult champion to face in uncoordinated situations, aka soloQ. Aatrox really thrives in fights where he can hit a tonne of people at once while they move towards him, hes a kite champion basically, if you just run in a straight line towards him and he retaliates by Qing your entire group, then no shit he's going to heal for a crap tonne, since your team positioned in such a way which hes designed to win. Usually the situations where aatrox overheals so much is often when hes hitting multiple squishies with the empowered Q. If he was only hitting one of you with his Q, then he would likely not be healing enough, if you and your group was tankier, then he'd also be healing less. Greivous Wounds alone isn't enough to make his healing just magically go away, you still have to play smart and not let him bait or kite you, especially when approaching with multiple people.
Funnily enough, I generally have the opposite feeling regarding Aatrox's healing, tho with a few caveats. I generally find his healing vs tanks to be so pitiful that its a joke, since both my damage and healing is inhibited versus them, it makes them much more difficult to try and fight if im on even grounds. To be fair tho, if I'm against multiple squishy champions without armor, I start frothing with anticipation to get into teamfights.
To sum it up. Heres some things you can do to shut down his healing:
- Approach intelligently. Don't just run up to him in a straight line and expect to be ok. Flank his sides, dodge around him, force him to awkwardly position between you so his Q won't hit the edge.
- Greivous Wounds. While it wont completely shut it down, its very noticeable when an enemy HAS greivous and when an enemy LACKS greivous, as an aatrox player myself. While i can still sometimes drain through opponents who are massively behind me or weaker than me, or who just blindly run into me, i have to play a lot more conservatively when i DO have greivous wounds, since it makes hitting the sweet spots even more important, as all my healing effectively comes from those sweet spot hits.
- Tanking up. Guardian Angel, Thornmail, Deadmans Plate, ohhhh man. Items that have armor absolutely cripple Aatrox's healing. The difference between fighting a tank and a squishy is night and day, since that 80% physical damage reduction also means "80% less healing recieved from me".
I know this was likely a knee-jerk reaction post, since i assume you just played against a fed Aatrox who carried, but I figured it might help if you had some insight into why the healing works and how it gets calculated. Lemme know if you have any other questions.
Also um.
Like seriously how is it fair for him to hit someone with passive and heal for 800 while under grievous wounds?
That would mean he hit a target with 0 Armor and 14,000 HP. Hyperbole is not welcome in conversations like these, friend. It just makes you look salty.