Conqueror is a result of the same kind of oversight in design logic that created 4.20 Weedwick.

For those of you who don't know: 4.20 was the patch that introduced red smite. That iteration of smite did a FLAT AMOUNT OF TRUE DAMAGE ON-HIT when smiting someone. Obviously this was abused the hardest by champions that could apply on-hit effects rapidly, while being relatively shitty on champions with slow auto attacks. How do you balance such a mechanic on every jungler that wants to use red smite to duel? You fucking don't. Old Warwick's ult was a point-and-click version if his current ult that applied on-hit effects SIX TIMES. Meaning every time he smited someone it basically bundled his ult with a free rapid ignite. The damage of the item was not only nerfed as a result, it was changed to be a DoT that refreshes with each auto instead of giving flat damage per auto. This somewhat normalized the strength of red smite across champions, making it significantly easier to balance.

To relate this to conqueror: It stacks from every individual hit, spell or AA. It is incredibly obvious that such a system is going to be abused the hardest by the champions that can cram the most instances of damage into a small window to instantly stack it while being shitty on champions that have damage that isn't so spread out among rapid individual hits. You can even look at top lane stats and see that a lot of the current best bruisers are the ones that can stack it stupidly fast, while the shittier bruisers are some of the worst stackers.

This is a rune that cannot be balanced for everyone, you either have to:

• nerf it down until it becomes "The Riven/Aatrox/Jax rune" because it's balanced only on them and shitty on everyone else
• nerf the champions that synergize around the rune to the point where they can't use anything else effectively, killing a layer of strategic diversity for them
• keep it in a state where it absolutely disgusting on the champions that abuse it the hardest so it can be decent on others

The way it stacks needs to be changed, not the numbers.