Yes Storm's Path mitigates magic damage too. It's very good on Leviathan EX waves that damage all the party, for example.

Most (if not all) relevant bosses have physical and magical attacks, so in theory Storm's Path is better than Rage of Halone.

Please note that while PLD only has 1 full-combo, which is aggro and debuff, Warrior has virtually 3, and only one is a full aggro combo, the other 2 are debuffs which should be up all the time, specially Storm's Path.

The PLD dmg mitigation and WAR increased HP and cure potency even out.

The biggest difference comes from Stoneskin and Adloquium. For these the increased HP make a hell lot of a difference.

A good White Mage will always Stoneskin a Warrior who has used Thrill of Battle, and regen a WAR/PLD who has activated Convalescence.

Also don't underestimate Marauder's skills such as Bloodbath, Fracture and Vengeance.
Together they heal you thousands of HP while active and Vengeance also causes damage to enemies attacking you.