Straight up. The game is expecting you to use all the tools in the arsenal otherwise you getting clapped. Or you can play like a ho and get the dlc that lets you be 10-20 levels higher than everything
Buffs, debuffs, nullifying skills to delete enemies turns. You can the dampener items to block an attack of a specific element. You can't guarantee what skill the boss will use but if it works out correctly you take no damage and they lose their turn
For the first boss you already got access to defense down for the main character (Aogami Type-1 Essence), Neko Shogun and Daemon (and whatever else you want through fusion).
If you're not applying defense down + attack up you're adding minutes to the fight. Time you can get clapped in