Rethinking Aatrox's Passive

Whats up everybody, this is my very first post so hang in there and be gentle.

First off, Aatrox is one of my favorite champions in the game, but i don't play him much due to his squishiness and lackluster passive. While i am confused as to why someone labled as a tank can be so squishy, that is not my biggest problem. Its the passive

Just to be clear, Aatrox's passive is called Blood Well and is described as: "When using an ability that costs Health, Aatrox stores the self-inflicted damage into the Blood Well. Upon taking fatal damage, Aatrox extracts the blood from the well and recovers it as Health over a brief duration. Additionally, Aatrox gains 1% Attack Speed for every 2% blood that is in the well."

Although this is a very interesting passive, I find it absolutely useless. Everytime I've had it activated I end up dying. All the enemy has to do is wait a few seconds and then finish me off 'cause the health recovered is so little and I'm so squishy.

This got me thinking. I like the idea of storing something into the blood well based on the amount of self-inflicted damage and then extracting that when he takes fatal damage; however, i do not want it to revive him and restore health. Instead I was thinking about making it work similar to Tryndamere's ult. First, they are sworn enemies so this would make thier relationship all the more interesting. Second, it might help negate that squishiness that gets so annoying. However, I dont want it to be a set amount of time like Tryndamere's ult. Instead I would suggest that the amount of time Aatrox goes invincible be based on how much blood is in the blood well at the time of taking the fatal damage. I also think the attack speed bonus can stay, 'cause thats the best part of the passive right now. I would also not change any of his other skills at the moment, 'cause I really like his kit right know. Although if I could dream, I would add a singularity pull to his ult to bring all enemies in toward him (similar to Orianna's ult); but thats just my dream.

I personally love this idea, although I'm extremely biased. So, How does it sound? Could it make him too awesome? I don't think so, if it is done right. I think of Tryndamere's ult which is OP only when used by someone that really knows how to play him.

Anyways, I just wanted to share my thoughts, please discuss and let me know what you guys think. I would love to hear from an actual champion designer, that would be awesome.

Thank you for your time.