Their healing spells are cheaper than most of the healing spells the other healing classes similarly use, plus you have a biggest MP pool. I normally don't have MP issues as long as nothing goes seriously wrong (and for a long time at that), like a pull doing too much damage or when the team is failing to evade avoidable damage.

I don't know if you do this, but I hope you don't:

You can do the tank a favor by NOT taking damage for them. It's bad for everyone if you have to heal yourself. The more players you have to heal, the more MP you drain and additionally the less healing your tank will inevitably get. Don't eat the orbs. Unless it is completely unavoidable. Remember your #1, they live only because of you, so if you die, then who's keeping the rest alive?