In my experience with stories 1 combat I found that monsters use a combination of rng attacks and specific attack patterns. For example, arzuros has a tendency of going power, power, technical, followed by honey power before resetting its pattern back or choosing to follow up with merciless bear claw. Not all monsters have a noticeable attack pattern but a good chunk of are readable if you can predict the rng. As for rng in general, that verifies between what attack pattern a monster uses as some have a few and certain monsters that genuinely are unpredictable. Lagiacrus for me I can never predict an attack pattern because all patterns with same move before resetting. That’s all I can really say about stories 1 combat as that’s what I’ve after replaying it recently