Google the word theory. I'm sure there's a definition of the word posted somewhere.Where do we have proof that humans are supposed to evolve into the Q?
A theory is a framework to explain a known thing, such as the theory of gravitation and the theory of evolution by natural selection. We do not know that humans in the ST universe evolved into the Q, thus your use of the word theory is incorrect. You should have used the word hypothesis. It's a common mistake.
As for the Prophets, it is a matter of faith. Gods and religions never seem to have proper explanations in the real world, so I see no reason why the writers needed to give an explanation for the Prophets. Maybe they were gods, maybe they were just highly evolved beings that were mucking about with stuff they didn't understand. It is up to you to decide.
Main Entry:the·o·ry

2: abstract thought :
6 a: a hypothesis assumed for the sake of argument or investigation b: an unproved assumption