Its channeled so the only class that really gets the benefit from immunity is paladin which isn't all that different then flash healing while bubbled. There are enough debuffs that hunters won't get the benefit from aspect of the turtle. Mages obviously can't cast it while iceblocked.

With druid its the same as paladins. You stealth and escape but your saving mana and maybe like 1 to 0.5 seconds. With mage its no different then invis to eat only faster. Its a benefit but not a game-changer for either.

Rogue probably gets the most benefit since this is basically a triple crimson vial. But with the 2.5min cd I'm not sure if it'd be ridiculously broken. And obviously the other team is going to see your a zandalari rogue and try to prevent you getting benefit when they vanish to recover.

I'd argue in its current state the velf racial is more powerful for more classes. Basically any caster gets great benefits without spell pushback. That is amazing in both pvp and pve and its definitely underestimated.