Yeah, but this is a rpg game where the character is, in-story, just THAT strong. You know how every scaler in internet vs battles make it so the character they are defending is always at their best and it is stupid when they trip, so if they can blow a galaxy, then it is just logical that they are always operating at that level? That's the logic aplicable here.
Also, ancient laws forbide them from reciving help, yadayada. The problem is when said ancient laws aparently don't protect them from asshole brothers sabotaging them.
It's not an award winning story, but as far as h-games go, it's very far from the worst. Also, this is an old game that Kagura took ages to translate since they took it as a project. By today standards, it's not THAT good, but when it was released, it was.