It does not generate True Damage from nowhere. It converts 8% of your damage TO true damage.
That means you lose 8% Normal damage, and gain that amount in true damage.
It also only starts doing this AFTER you've hit an enemy 5 times. For most champions this means most of your kit is already on cooldown when you finally activate Conqueror.
It's not fucking overpowered, it's up there with the weakest keystones in the game. And pretty much most of the champions that currently take the keystone really shouldn't.
Also during a game when looking at the scoreboard if you mouse over peoples keystone you can see their statistics.
The top number that reads "Total True damage dealt" is **_NOT_** the important number!!!
Its the middle number that says "True damage that **_WOULD_** have been mitigated. This number is what damage Conqueror is ACTUALLY adding that you wouldn't already have done. Because remember, it's a CONVERSION.
And yet I'm still waiting for most people here to completely misunderstand what the keystone does and flame me calling me 1 IQ.
If at least 1 person reads this and is educated then worth it.