I'm sympathetic to this.... I wasted ampies on 2* girls. I felt like I wasted lvl 100 manyus on 2* girls. I started a new account to "undo" this. Even on my main account (the restarted one), I'd do things differently now that I understand the game.

For instance, I'd have started farming event girls immediately. I'd have bought storage space to save ampies/manyu while I farmed event girls. I'd not have wasted ampies on 4* girls. For instance, Edelwiess is an extremely powerful event girl in bloomed form. I'd have been careful about my farming and tried to balance slice/pierce/hit/magic girls so that I always had a 5* to level up.