I have various racial and regional pantheons that have gods that cover the same domains. IMC, "As above, so below" as there is a spiritual world where all the gods, paragon creatures, and much other weirdness exists. The lower, material world mimics this world to some extent. The darven and elven gods have produced dwarves and elves in the material world. Later, human gods were born and so humans came to be in the material world. This is also where things like owlbears and such weird magical creatures come from. In the spiritual world, things aren't as bound by biology and an owl and bear and have union and produce a vaible litter of owlbears that might wander into the material world and reproduce as a new species. Half-elves exist because an elven and human god got together and had a child. There are no half-dwarves because no such thing has happened in the spiritual world. While there are realativly few gods, there is nothing keeping different gods from having the same domains as there are keeping PCs from having the same classes. A pantheon might be composed of all gods dedicated to war just as an adventuring party might be composed of all fighters, but typically they vary for similar reasons.