Yea, I can understand that. This game just isn't set up for difficulty outside of boss fights so wanting things to be actually challenging outside of that is going to be a nightmare.
The problem here is that this would punish new players for not making perfect builds and taking away their means of making additional builds. Like now I know fairy is completely inviable against primed explosives so I should go for a different starter deck.
I suppose one thing I should say is that I really appreciate the beginning height increase letting me immediately grab a deck other than the default starting deck of cards meant for a very different game.
I think late game it's fine for the cards you added to exist since the player should have many options by then and some extra hp by some method, but having the contestants get big so quickly (which I assume is the trigger for thunder hammer to appear) makes things pretty bad. Primed explosives is still kinda bs at the start though.
Good luck whenever you get around to looking at the balance again.