Actually enhacement shammies are doing pretty well in arena atm, they are pratically always prefered over a dk, especially with the purge/off-healing advantages. Besides, you were never the only caster spec that get's trained everygame. Boomkins also suffer pretty well, and that wouldn't change even if they got more defensive abilities, since they represent such a threat in terms of cc. Just like boomkins, elementals can be pretty destrutive if you don't control them.