I agree with you 100% on the first part of your post. But when it comes to girl on girl, in my opinion there can't be enough of that and the MC doesn't miss anything. In addition, threesomes without active girl-on-girl activity are extremely boring. The MC cannot please all his ladies in his Harem at the same time, why shouldn't they have fun among themselves? That, at least in my eyes, would make the whole story livelier. It cannot be assumed that some of them will suddenly become hardcore lesbians (although that would be fine with me).