You kind of forget that Eric isn't the MC of the game, but instead Max is (or at least that was the game says). So making paths for Eric being in the game should be the other path that should be worked ocasionally, since the game goal is for MAx to get with the girls, keeping Eric in the game is just a way to slow down progresion with Max and the girls, so that's why Eric should be gone as soon as posible, so we can finally get the sex scenes and normal scenes centered around the MC, not a secondary character like Eric, who was only there because DS didn't understand how incest works and he thought that it was just watching your family fucking, so the original plan was to make an incest game, and in an incest game Eric has no place tbh.
At some scale you are right, i think there has to be way to get rid of Eric easy so Max can go fuck someone as fast as he can.
But there should be way to be with Eric, if you want good story Eric was first one to change Ann thinkings of some sexual things. Eric changed whole story if you ask me, who knows will Ann do anything that she done after Eric if he didnt change her. Her pespective about some thing in their incest sex things in family will be more efficient if he changes her more and that can be done by just making Eric better path