Flawless victory doesn’t effect every battle in the game (outside bonus XP & G), only in some boss fights does it have story relevance. It’s usually always mentioned in the immediate aftermath of a battle, though.
Also, there will be a spell counter system, though I plan to make it harder to get perfect counters than perfect deflections, but I don’t plan to introduce spell counters until a little later in the game, so there will be sometime where your best bet for a flawless will be to use madness or lust (or both) and, if necessary, save scum. It is luck based, but I also think it’s contingent on efficiently building up auras. As the game evolves, I hope consumables and additional types of equipment will also be able to contribute to these strategies.