Personally, I think the Olga thing just makes the game more realistic. Sometimes, there is either no completely happy ending. Olga needs MC to be totally devoted to her, and given the parameters of the game, that isn't realistic. So one can play the Olga route, and it would feel somewhat unnatural, or he can do the natural thing and create a quasi-harem.
Its a kind of catch-22 that is more lifelike than a game that allows you to do whatever you want with only minor consequences. And, for a game about vampire, mermaids with pussies and no tails, etc., its a pretty realistic touch.