Is %Health damage something we should start worrying about?

I just can't tell whether %Health damage is a problem, an indication of another problem, or a good solution to a problem.

It comes in three flavors:

• Current Health damage, like Mundo's Infected Cleaver or Elise's Neurotoxin- Current Health damage is good for wearing down the opponent, but needs a flat base damage or a minimum along with it to be worth much, otherwise you'll try to finish someone off and only hit for 10 damage.
• Maximum Health damage, like Koggles' Bio-Arcane Barrage or Vayne's True Damage Max Health Based Effing Silver Bolts- It is useful ALWAYS. The presence of Max Health Damage in a match makes armor/MR and penetrations more important, because buying flat health doesn't slow down how fast that source harms you.
• Missing Health damage (better known as Execute damage), like Garen's Sky Sword Justice Laser or Jinx's Super Mega Death Rocket- Execute damage is obviously very good for finishing someone off, and it's a neat way of giving a character a big hit that feels really powerful even when behind, without letting them use it to wipe out 30% of the entire enemy team's health at the start of every teamfight.

So, what first tipped me off that something was weird with %damage was the whole top lane situation. Shyvana got a minor rework and went from "pointless" to "Consistently able to pummel lane opponents down". That change was to make her Fireball's mark deal %Max Health damage on every punch. It's amazing how much that helped her! Amazing enough to make me kind of suspicious, really.

Jinx was released. Super Mega Death Rocket has Execute damage, which makes sense when put alongside her passive. Then I hear someone mention that Graves would be a really competitive pick if his ult had execute damage too, and I agree and think "Wait.. percentile damage again?"

And I think back to Sejuani's rework, and the thing that stood out to me most about it? To try and make her viable- her boar charge gained %Max Health Damage.

[EDIT FROM THE FUTURE] And I started writing this giant essay when I read someone's concerns about the Nidalee rework having trouble fighting big beefy guys without her trap's resistance shred. The answer was "Probably %Health damage"

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%Health Damage isn't really a special niche thing anymore. It's not one of those weird cool perks that only a few characters have, it's a core part of many champions' kits and a perk of three major items! But I'm seeing it thrown onto people as a way to make them viable, and that just tickles the back of my brain, makes me think there's some other problem that %Health stuff overcomes easily. Something, somewhere in the world of Defense Stuff, something must too big. So big that the game needs all these sources of damage that scale off the target's max health just to keep up with it.

But I don't know if that's a problem. %Health damage is widespread now, for better or for worse. It's a part of the game!

Something still stinks though. I wonder, if you took most of the %Max Health skills in the game and replaced them with Current Health or Execute damage, what would happen? It might reveal what still needs to be tuned among defensive stats. And I think it would be worth a shot- %Max Health damage is kind of dumb to be so prevalent. The other two kinds of Max Health damage have some thought and gameplay around them, at least.

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Enough of my indecisive blather. What do you think? How is %Health stuff affecting the game? Are there things in the game that are held back by it? Is it holding shut the gates of hell? Should I have used a bunch of champion and item icons in my post?

The world is a mystery.