What's the appeal about harem setups, anyways? Are readers supposed to connect with the MC? Or is it more of an opportunity for readers to shop out of myriad girls?
A bit of both. It really depends on the harem. Some harem setups revolve entirely around their MCs and the girls are used to show off how awesome they are (like SAO and Mahouka). Others try to give their MCs as little presence as possible to encourage a different sort of self-projection, like when you read your own traits into a blank slate protagonist in a game, for instance. Either way, I'd say the harem fantasy is all about masculine empowerment.
