My personal pet theory is that both could coexist.
Greek, Norse, Egyptian gods are mostly the same. Several gods with certain jobs they do and values they represent, and one leader. You can see that pattern in a lot of religions across the globe.
Then there is that other god. Perhaps he belonged to the other ones but was exiled or he was just miserable and hungry for power. He picked a certain group of humans and he told them that he is the one God, and that all others are false Gods. With many cheap parlor tricks like burning bushes and all that, he managed to start a revolution.
I guess the Christian God fought a battle against all the others, and maybe he won. Or the reason why we have never heard of any of those gods in the last 2000 years is that they all killed each other. You could kinda go a bit sci fi with that story.
Perhaps the final option he had was to take human form and tried to hide amongst humans. And guess who nailed him on a cross: Romans who believed in the other gods.