Rubbish. And the first boss that can drop a limited edition girl gives 2 exp? So, you have a choice between going back in the hopes of getting lucky (may never happen during event), netting almost no exp, so no levelling and therefore having a smaller energy and battle bar which gives limited chances and slow story progress, or moving on to level and progress, but have no chances of getting a rare girl. Or, third option; lots of micro-transactions! It is manipulation by design.
I have no problem paying for a well made game, I actually enjoy contributing and giving back to creators. That instinct shuts down the moment I see crap like this. If you enjoy the game, good for you and long may you continue to gain some pleasure from playing. However, don't pretend that the nonsense clearly being pulled is alright just because you accept it. I don't, and I won't. No money from me, ever.