While turning [Light] into something that can grow by digesting [Darkness] would be quite a complex matter.
Even for a whole world, anything is possible as long as one is willing to pay the price, and even the opposing Source Powers can be forcibly changed.
But such an act clearly isn't very meaningful, so when the remnants of the Nine Realms were integrated, it more so resulted in the strengthening of their respective powers.
Of course, the uses of the internal circulation are far more than these, and the world is not limited to ascending through externals.
From the very beginning of the world's creation, Chaos incessantly birthed new concepts, new Godhoods, advancing the procreation and evolution of All Gods and even the prosperity of All Spirits, which is essentially another way of amplifying itself through the world's internal cycles.
And of these profound mysteries, Zeus was not very clear.