As for gods and all that, I agree with the notion that it really depends upon what the basic assumptions and cosmology of the campaign world are. What is the nature of gods? Are they the embodiment of cosmic and natural forces or highly evolved beings? Etc.
For the sake of a role-playing, in he question above I prefer the latter approach - along the lines of the Thor movie in which the gods are more akin to very powerful extra-dimensional beings that probably evolved to that point, whereas PCs are more akin to superheroes that are either "mutants" with inborn powers that they develop (arcane spell-casters) or mundane heroes who are just really good at killing things (the Batman types - rogues, fighters, etc), or gifted by those same extra-dimensional beings to be their agents on earth (divine spell-casters).
As someone said above, mortal PCs also have that "hero factor" which isn't solely the purview of D&D but exists in movies, books, and myths for thousands of heroes. Think of the Greek heroes who prevail against titans and gods; now many of those heroes are demi-gods or have some kind of divine lineage (usually through that old perv Zeus), but they still win out not because of overwhelming power but a heroic quality that allows them to do crazy things.
But there are so many ways you could make an interesting cosmology that frames the game in different ways. Maybe the gods are highly evolved extra-dimensional (or planar) beings that draw power from the worship of mortals but also keep them capped in terms of power lest they challenge their rule (or figure out the truth of things). Maybe the gods send nasty divine assassin-creatures to kill off any PC that becomes 20th level, which gives an actual rationale for capping levels. That would be a fun way to end a campaign! And if the PCs survived, then they'd have to face the gods...There you go, imagine an epic tier campaign in three parts: Fleeing the Gods, Facing the Gods, Becoming the Gods.