First of all, this is not a romantic NTR. Hunter is not interested in romance, but in pussy. Also, in the canon version, Hunter is more blueballed than Sterling is. The villain is always one or two steps ahead, because, hey, he's the villain. He's the one with the evil plan. There's a reason why the most memorable villains are the most heinous ones. No one remembers the incompetent villains who are one step behind the good guy. That's not a villain, that's just a glorified henchman with a superiority complex.
Also, Sterlin is not using corruption, he is being corrupted, just like everyone in the house. The stuff he's doing isn't what he would have done at the start of the game.
I take it you never saw a Tiroler movie. These types of movies made in the region of Tirol (the german speaking part of Italy) were famous for their slapstick humour in their sex films. That's what we have right now in this game, humor in a hardcore porn game. I don't care about NTR, but if there would be a non-animated sex scene, no matter who the participants are, while all the rest is animated, I'd feel robbed. Also, why can't Sterling fuck the other characters as hard as he fucks Eva? I don't know, maybe because he isn't fucking anyone else yet, other than Malory, who he also fucks hard, so I don't get what you're saying. It's not like he fucks someone tender in the game. And the anal scene with Brenna was also far from gentle.
You're just complaining for the sake of complaining without any basis, just because Hunter is a well written evil mastermind and you can't stand that Sterling has scrupules while Hunter has none and goes straight for the pussy.