Conqueror change proposition:

"Every time you damage an enemy champion, you get a stack of 3 adaptive force for 5 seconds. You can get one stack every second. At 5 stacks, for 10 seconds, 10% of your damage is converted into true damage, you get 5% movement speed while running towards enemy champions, and you heal for the true damage given to the enemy"

This ensures champs can't insta stack conqueror, and instead have to actually be in prolonged combat. Naturally, that means some champions will lose some more hp as they aren't able to stack it as they once did, but if they do hit 5 stacks, they can heal it back up with their normal fast combos. The 10 second activation window is to ensure that conqueror isn't abused, granting over 700 health or something in a single teamfight, but rather should specialize in one on one combat. The 5% movement speed buff towards enemies is to ensure enemy champions can't as easily camp out the conqueror activation time.

This style of buff should massively benefit juggernauts like Darius or Mundo, and deal with the problematic champs like riven or camille, while giving both champs the damage. It makes sure that champions actually commit to staying in combat, as opposed to getting 5 stacks in 3 seconds, doing a true damage trade, and then getting out.

My version probably isn't perfect, and I can already see multiple flaws with it. But thats fine, no rune should be flawless. There should be games where I play Darius, not see conqueror as a to go rune, and pick phase rush, aftershock, or grasp. Similarly, (ill use riven as an example) riven shouldn't always think conqueror is the best rune in all scenarios. If she wants cheesy burst, she should think electrocute or dark harvest. If she wants sustain, maybe grasp or aftershock. If she wants more mobility, perhaps phaserush. Does she want in lane sustain? Try fleet footwork.

This version of conqueror has flaws, but that just gives more opportunities for rune diversity.