Plus it’s just far more fun when players get to actually use the character building decisions they made. I think it’s much more fun to base enemy actions on what they can reasonably perceive. If someone has innate fire resistance, let the enemy sorcerer cast burning hands on them once to figure that out. If it’s a fabled and well-known Robe of Fire Resistance that they’re wearing, any half-intelligent spellcaster will know not to use fire spells on them, but the goblins with flaming arrows might not be so savvy.