Is Max % Health True Damage OK? (Not a Vayne Hate Thread)

Before I start, let me just repeat what was in the title.

THIS. IS. NOT. A. VAYNE. HATE. THREAD.

I hate Vayne as much as you guys, and want to see her nerfed, but this post isn't about that. It's about the mechanic that is max % health true damage. My honest opinion is that max % health true damage is the unhealthiest damage mechanic in the game. The idea is that if the enemy deals physical damage, you get armor. They deal magic damage? Get magic resist. Are they dealing physical, magical, and/or true damage? Get health! But what do you build when the enemy has max % health true damage? There's attack speed slowing items like Frozen Heart and Randuin's Omen, but guess what; their stats won't help against it.

Who/what has max % health true damage? Vayne (Everyone's favourite champion) Fiora Redemption (Hey, it's still preseason with no new patches, stuff's gonna be busted)

Let's say max % health true damage really is bullshit, what do we do? What do we fix? Rito plz don't gut Vayne she's my fav champ! (SARCASM) Best option is to replace the max % health true damage with someone else that does the same job!

She's a tank shredded, or at least she's meant to be. Perhaps she can receive normal true damage and gain attack speed when she gets the true damage off, sort of like Vi's W, except with true damage instead of armor shred. The idea behind Fiora's passive is that she's hitting an enemy's vitals through their armor. So either just true damage, bonus armor pen (lethality or % armor pen), or max % health PHYSICAL damage. Since it's a support item, having the damage scale with level won't work cause of how supports are always lower in experience. Perhaps a lethality-like mechanic where the true damage scales off the enemy's level?

I just needed to get this idea off of my chest and see what you guys thought about it, leave some ideas and opinions if you want to. Nothing hateful please!