Back in the day if you wanted true damage you had to take ignite or play olaf or cho'gath.
Now every champ and their dad seems to have it.
Why is true damage so common now? Also, why is it necessary when tanks are currently the least tanky they have ever been?
Three Years Ago.
Good luck. People LIKE True Damage.
Because items or runes. Could you imagine how things would be if they removed easy access to True Damage? I played through the Tank Meta. I refuse to go back to that. I already have to deal with teams who focus tanks just because they're tanks. Let me have my true damage, man.
I sometimes wonder what's the point in playing a tank when most of the damage you took is true damage.
Yeah conqueror is OP atm. Me and my friend did a video on conqueror and how OP the jungle role also is. Check it out https://www.youtube.com/watch?v=wFej9569s48&t=
Vayne's Silver Bolts are her way of hyper-carrying. Hyper-carries typically utilize some combination of %HP damage and/or AS steroids to chew through any target regardless of their resistances. Vayne has no AS steroid (on a champion whose entire damage output is auto attacks with no way to extend her AA range), so she has one of the strongest %HP damage effects to compensate.
Fiora has %HP true damage for thematic reasons. She's supposed to be able to out-duel anyone 1v1 by playing well and hitting the vitals. The whole idea of a vital point is striking through her target's defenses. It's either %HP true damage or a large amount of (bonus) armor penetration, and at that point the true damage is honestly simpler to grasp.
As for Conqueror, it's good in concept but the execution needs adjusting.
Reduce the true damage conversion to 10%, but it scales up to 20% based on how much higher the target's Max Health is than yours. It's supposed to be specifically aimed at fighting beefier targets, after all, and the effect makes more sense here than on Cut Down (you know, that rune in Precision that I'm pretty sure literally nobody uses).
Make the conversion adaptive, meaning only your dominant damage type benefits from it. Hybrid damage is already pretty anti-defense as it is, Conqueror doesn't have to double down on it. This is mostly a Jax nerf, though it does hit Irelia too since she has P/E/R for magic damage.
I made a post with this as one of the points a brought up because it's been an issue that riot once upon the time said they were poignantly trying to avoid though thats been completely forgotten. But people on these boards don't care, a lot of them are the people who the watered down nature of the game is catered to.
True Damage isn't common.
It made 
E way less special too
Because idiots think that because the tankier tanks are more pronounced compared to their counterparts that tanks are more tanky not less tanky.
if they nerf conqueror everything will be fine for tanks ; i mean when i fight a tryndamer , fiora or riven , jax befor conqueror procc , i'm always like : oh yeah i can out trade them ; the conqueror procc in 1 sec if i dont flash i'm gona probably die
