The MC is actually not too overpowered (at the moment) and not ungrateful or unkind. The people that helped him get where he is, he never forgets them, even if he is looking for benefits. Also he doesn't really hide that he is going for the harem route, especially from his first wife who is more about getting stronger than being his wife. They both initially have no feelings for each other because neither had a choice in this marriage, so they just decide to do their own thing while married.
The MC is actually not too overpowered (at the moment) and not ungrateful or unkind. The people that helped him get where he is, he never forgets them, even if he is looking for benefits. Also he doesn't really hide that he is going for the harem route, especially from his first wife who is more about getting stronger than being his wife. They both initially have no feelings for each other because neither had a choice in this marriage, so they just decide to do their own thing while married.