I think that may be the issue. I like lesbian content and all, but it's just that usually with these games the women are typically always bisexual. Granted, it's a fantasy story and all, but it's based in the real world. The amount of women that are bisexual (even if guys joke that women have a higher tendency to be so) isn't so high that the MC is surrounded by bisexual women and only them. Most would be straight. So the fact that, even if it was a polygamous relationship (seeing as this will probably turn out more of a polyamorous one), not all the women would be in relationships with the other girls too.
Depending on the size of the "harem," or I guess in the case of this game, the open relationship's members, it should have two, maybe three women who are bisexual and intimate with each other as well as the MC, and the others would be strictly on the MC only, minus willing to be in a threesome with limited interaction with the other girl. But, that's just my opinion. It's still a fantasy game, but since it's based on our Earth, countries, politics, culture, etc., it would give the game more realism with the fantasy elements to suspend our disbelief on other things.