I think harem is a fascinating topic that isn't explored in a serious manner enough in media. It's often used as wish-fulfilment fantasy and comedy. For a more tonally serious story like CoMS, the concept of harem can be explored better through the eyes of the females. The inherent imbalance of the status quo has a lot of potential when it comes to conflict and growth.That you have this expectation is understandable but also quite sad. There is no reason at all not to have backstabbing and betrayal in a harem. Often developers think only a state in which everyone is content and happy is proper harem. But imho that's a lack of creativity rather than a rule of nature.
To put it in another way... What's the point of a harem if you didn't have to go through hell and back to earn it? Where's the satisfaction if the girls just fall into your arms by the force of nature? Comedically it works, but the moment the story takes a serious turn, it all falls apart.
Anyway, I'm just elaborating on what you've said and I'm trying to explain my perspective and how it concerns CoMS using your comment.