Well, for one, they didn't actually need to attack large areas.
If they could locate the monster's core and simply snipe at it instead, then they could even focus on using the tiniest stones. The same went for those creatures with obvious wings. If they could target those specific areas and bring them down that way, then they'd be able to conserve as much spiritual energy as possible without putting too much strain on themselves.
Honestly, if they could only use their space buttons or access the dungeon inventory, it would've been nice to take out the underwater pocket dimension. Then those with water-based attributes, like Killian and his tide, could maybe just flush the grounds!
Sadly, none of those options were in the cards for them, so they'd simply have to improvise.
Then again, Luca wasn't planning on taking down every enemy to begin with. They only needed to clear enough of them to create a relatively safer path toward wherever the core might be.
