---- I cant believe Im addressing this song in such a way, but 'Aint no fun' doesnt necessarily imply group sex. I guess it could be inferred, but I always took it to mean that you want the female to be a bopper, and go from nikka to nikka individually. Like if she comes around if a nikka from the crew wants her, then she needs to bust it wide open and shes nobody's girl in particular.
I agree with most of your points except I gotta nitpick this one. I don't think the song's about group sex but it also doesn't make it any less questionable, it just makes it less overt. Like ultimately it's still about the pleasure the men are getting, the woman only matters insofar as she can be fukked.
Though that's probably not your point anyways, it seems like you mostly had a problem with the song being perceived as being about group sex.