I'mm'a be real, I think it was less that the combat is easy, it just felt... insubstantial. Just pick the easiest fights, spam whatever your best move is until the end of time, pick a different move if the opponent is resistant to it, repeat until all scenes are unlocked
I mean I suppose that's how it works in the real Pokemon games too, but IDK. Not really sure what could be done about this, either, since having to put in actual effort into fights would make the game take longer and probably be a bit of a drag, since the fights themselves aren't the "sexy part" of the game, but then a mindless grind isn't fun either.
All I can really think of is the possibility of some kind of actual dungeon crawl to break up the combat, exploring random-generated dungeons (even if it's just [EXPLORE] [LOOK FOR FIGHT] [EXIT] text stuff and not a real "map", maybe culminating in a "boss" fight if you explore enough?) that can have random sexy events pop up, rather than just repeating fights forever until everything's unlocked.
Either that or go a bit deeper into the "porn" side and add post-victory sex mechanics for bonus XP, I guess.