GalacticStorm
Smart Alec Know-It-All
You'd never get both of these entities at the height of their powers because as one prospers and grows in power surely the other ones power fades. The Chaos King must absorb creation to reach the height of his power and the energies of the Phoenix Force are creation. So when the Phoenix Force is reborn the Chaos King is reduced in capacity and when the void takes over creation the same goes for the Phoenix Force.
If TOAA somehow made it possible for both entities to exist at the height of their powers then it would be a stalemate. Neither can die, only be reduced in capacity.