Unless I'm doing it wrong, I *do* put barriers up. I handle the mage usually and let the melee/ranged guys do their own thing. First thing I do when combat begins is put up a party barrier.
Problem is, the barrier comes down off my party members pretty quickly and the ability is still recharging. So they'll stand in the way of fire coming out of a dragon's mouth instead of moving (unless I manually take control of them to move them when I realize they're burning alive).
You have to use Barrier when the big AoE comes, and then hope it's recharged for the next. Don't use it unless needed. You might also want to use the various elemental resistance belts. If you're having trouble with the breath attacks, you might just want to use less melee characters.