Is there something actually more OP than %Max HP True Damage?

Yes - shields.

Seriously, shields are the only counter to %Max HP True damage... and there's really no counter to shields (I mean, you can attack someone else or just fight through them, but neither of those are a good option if you really need to kill that target before it busts up your carry / yourself...). Frankly, I'm somewhat okay with shields being so busted right now because at least not being able to kill someone is better than dying to someone no matter how tanky you are... but really ideally neither of these would be OP.

I think in order to nerf shields, we need to first nerf percent max hp true damage. That really needs to be conditional. Something so powerful should not be an inherently free part of a champions kit - it should be tough to land. Not a 3-auto-attack that really is 1 and two abilities ( AA-Q-AA-E). Vayne's not even really OP in my opinion - just some extreme usage cases feel really bad.

Let's get in to shields though. Seriously - there are way too many, they stack way too hard, and they counter literally EVERYTHING. The huge majority of damage in this game is telegraphed and delayed. There are very few abilities that deal damage instantly where an ally can't react with a shield before the damage hits.

I mean, isn't anyone else sick of Poppy tower-diving you pre-6 just to poke because her passive shield blocks the TWO turret shots plus any retaliation damage you deal entirely? Even when she misses the stun on her charge because CotC procs on the displacement alone? Like seriously?

Or + any of followed up with making that ADC you just 100 - 2'd suddenly unkillable then at 80% health again?

Like, it's nice that there's counterplay to % max HP true damage. Getting a massive shield on you is a great way to stymie that . We seriously need to reconsider how this works though.

Is the answer to simply give shields the slow treatment of S5? I honestly think this would be fair - at least put some skill in to it. Just like how slows were no longer allowed to stack - why should shields have EVER stacked? It would be more optimal for the shielder's to reapply each shield right before the previous one wore off ( / was killed off) as it would increase overall duration - yet with the huge duration on all the shields in this game they just all get unloaded at the same time.

We need 2 nerfs to shields: First, they need a shorter duration. Shields should be reactive to incoming damage. Not a catch-all to a fight where if a shield is on a key target you can't just wait it out because that target will kill you before it comes off. It should be an option if your opponent shields too early to hold your abilities for a bit then crush them for the mistake.

Second, they need to either not stack or be less effective at stacking. Either 50% effectiveness for additional shields after the first (similar to 's debuff) or only the strongest shield applied has any effect (like slows). So if you get a 400hp shield and it has 375 of it eaten then a 200hp shield is applied on you, you have a 200hp shield, not 225. If the 400 and 200 are applied at the same time, you get 400, not 600.

Don't do this until you fix percent max hp true damage though. Shields are the only thing holding that in line...