I'm not the biggest fan of Harem games, but I liked a few in which the Harem is on the smaller side. Like you said, it's really hard to make them even "semi-realistic", maybe in a fantasy or medieval game. That's why I prefer throuple relationships to pure Harems; while not the norm, at least they can be found in the real world, and it's easier to make them appear natural.
As for obsessive Harem fans, and I'm talking as someone who dislikes NTR, nothing makes me laugh more than when they complain about LIs already in the Harem interacting among themselves. They perceive sex between girls (with or without the MC present) as cheating and constantly complain about the MC being NTR'd.