Something I've seen is people misunderstand about spells in tactical combet.  You only need one action to cast a spell, but it uses up all of your actions.

So you can attack with all of your actions except the last, and then cast a spell.

When comparing the value of a spell, you don't compare it to all the attacks you can make in a turn, just the last.  And since a spell ignores defense, it's really great late in the game - as long as you attack physically with your other actions.

Hence a mage also needs to be a warrior.  And a warrior would be advised to also be a mage.