Ok, it is true that it does not seem to be the most original story but we have to be honest, no game currently is, most of them are a young boy who wants to throw his mother and sister, or a slightly older man who goes to university and is He throws his classmates and teachers, or a mature man who fucks his daughters, however that does not mean that it is a bad thing, he should only raise it in an entertaining way and that's it.
As for what is really problematic about the game is the sandbox, many do not like it because of how repetitive it can be, however it is not necessary for it to be this way, games like Depravity, Milf city or Summertime saga are sandbox but the advantage is They are not repetitive since they focus not on scoring points but on each scene following the previous one, I would not rule out this game, I only recommend optimizing it in terms of gameplay, that's all.
Regarding that the MC could be an idiot who blackmails the girls ... it could not be so bad, of course it depends on how it is raised, there is a game (if I remember correctly) where the MC is a psychopath who hurts (physically ) to the girls and for many it is a great game (not my case, but I suppose it will be well built), the point is that it can be an MC who uses blackmail and deception to make girls become their whores, so that in the end they accept it, although this is just a theory without more.
Good luck Dev, and, if possible, could you comment on what tags are expected in the future?