I think at some point they discussed that the gods kind of choose what name they wish to go by. They've been called several different things throughout the ages, most choose what they like best.
Hercules and Thor are not cousins, but Thor and Set from the Heliopian (Egyptian/African) pantheon are cousins.
I think this is a hard one to compare - in the Marvel Universe, I think the Greek Gods were a lot weaker than the DC Universe. The avengers managed to zap a couple of them down in early episodes (I guess they could zap the Asgardians down too - dang plot queues!).
Marvel : Asgard > Olympians
DC : Olympians > Asgard
Myth : Olympians > Asgard.
I'd vote the Olympians in due to the fact that they all specialize in different areas - diverse attack plans, and with Athena on their side, and also - in the case of myth, they didn't have problems turning to Herc to enlist help (not too proud to use alternate plans). - Not voting for Ares to get any kills though 😉. Resourcefulness over straight attacks.