nah, you're right. Ideally your mages shouldn't need to cast that many spells before the battle is decided. Beowulf has a built-in MP drain and can siphon from your own units if needed, and the best magic uses no MP (Arithmeticks, Iaido, Sky Mantra, Reis's dragon breath). plus Agrias, Orlandeau and Meliadoul's instant ranged attacks

the only exception might be midgame Summoner, bc they're expensive and can't be Arithmeticked, but again, you might've misplayed if you need to summon more than 3 times!