No no
I'm just in an argument with someone who thinks it broken
If you're worried about the balance, you could read them as "when channeling that type of magic..." i.e., in a round when you're throwing fireballs, you're immune to fire but vulnerable to ice. In a round when you're laying down that blizzard, you're immune to ice but vulnerable to fire. You're typical fire mage might always have a little fire around her and thus the immunity/vulnerability is always on. Same with the ice mage and ice. But the switch hitter isn't in that situation. She channels one elemental power at a time. Just a thought.
Having said that, my personal opinion is probably to go with Morrus' 'immune to both'. The reason I'd see that as not unbalanced is because neither includes immunity to sword.
