Of course Hunter's existence serves the narrative, but calling that "cheap" is subjective. Hunter is the antagonist and source of conflict. There's a saying in writing: "there is no story without conflict." If Hunter wasn't part of the story then it wouldn't BE a story, it would just be a series of events, and that is boring.
Hunter is also the benefactor. As FoolishFool0 astutely pointed out, Hunter is the one to get his hands dirty, which means Sterling doesn't have to stoop to the level of other games' MCs while still reaping the rewards. That's why Hunter really exists, in a meta sense. These games are a fantasy, but in order to be even slightly plausible the MC needs some kind of gimmick or advantage that helps him easily seduce every female in his life. Such gimmicks are usually unethical and almost always contrived, but having them implemented by a villain allows the other characters (especially the MC) to keep a clear conscience.
What makes this game shine is the characters. The believability of the premise was never what made this game stand out, it was always a means to an end, so maybe try not to get hung up on it.