That's false, unless you have less than ~70VIT or less than 20k HP.
Wear a Golden Rod Orb and Golden rod Robe (10Mdef). The ORB -15% wind, Cranial, Combat knife, Red Pom Band reduction still applies when frozen along with your natural MDEF. You're still reducing >65% damage with your magic defense.
But you WILL die without a cranial on.
You're right. I forgot about the orb and the shoes. I still don't have a RPB, though... on my way to buy one this weekend, and try to +9 it...
I agree about the fireballs though. I never died to a single fb, but when multiple Celias combine their powers, it's really bad. As for the Thunder Storms, though, you've never been betrayed by your team's sorc? Like, you are killing a Celia, she sends a TS, you position yourself inside ME, then your sorc proceeds to trollface and move the ME a few cells, so that you get killed. Of course, these are not intentional (most of the time, at least), but happen all the time.