Hunters, they always seem to be OOM
But seriously i find it ridiculous how mana is so efficient now, I never dropped below 75% on my Ele shammy unless i was just spamming AoEs, but single target i finish a fight with 100% -.-
Even my Resto Druid has a seemingly near infinite mana pool, And i PvP on him, so even with shift spams and lots of casts and CC etc, It takes a long time to run out of Mana
As others have pointed out, Guardian was added for a reason, And adding these other "tank" and "heal" specs to other classes would be a big mistake IMO as in Raiding guilds people will end up having to play other Roles, Plus saying "they want more roles for the class they love" sounds redundant, because you love the class because of how it plays, if you add an entirely new role to it it's not the same anyway