It depends on the situation and where you are in the game. But to generalize and hopefully help, I'll chime again. I also have a video on youtube of my solo in Tactics.

The reaction that puts melee to the test is Blade Grasp. I usually rely on that with MagDefUp. That way my defenses are balanced in the end.

You can argue this character over that, this ability over that like I did. What would put magic ahead of melee in my opinion is it's versatility in 'all' the magic users.

There's no character totally invincible from magic in Tactics. Even a time mage could spam Meteor if all else failed and recovered with 'ITEM'.

Magic users also make best of the secondary skill. There are fewer skills melee benefits from. The most being equip change. But like I stated it's versatility in the spells over swinging a sword all day.