Being able to put up a bubble shield that lasts for a few seconds, once every 4 minutes, is not going to have much impact at all on your survivability. What will is your gear, knowing the boss's moves/warm-up animations, and skill. Playing Devil's Lair with randoms, I've been in plenty of groups where people will just die again and again to the tank's red laser. No bubble shield every 4 minutes is going to change that. Which is why when I'm raiding, I will not even look at class - it's utterly irrelevant.