I've briefly wondered about the same subject sometimes. There's so many mythologies where a division into two (or more) groups exist that it must have been a thing for a really long time. Not just Norse and Irish and Greek, but also the deva/asura distinction (and yaksha/rakshasa in spirits) of Hindu myth, or even the division of gods into original anunnaki and the later igigi in Mesopotamia - much like the later Greek division if you only consider Olympians and then non-Titan 'other' gods.
There's definitely distinct groups of gods, but what those groups are equivalent to in human societies...well. *shrug*