When you heal, you can know if it's a beginner or not.
Most of the time in high level dungeon they speak up and say they are new
Plus new player are most of the time using more cooldown than they should and it's cool to heal.

In low level dungeon you cannot full DPS and heal as easier as it is in 50/60
Because eof the sync that lower your spellspeed or lock some useful spell

There is no excuse for a tank to not use his cooldown. Which is what he should do as much as i have to use my healing spell to keep him alive.
Plus only 25% of the team will be derp, if i'm not healing i'm dpsing my Ass off... So it won't be a problem the pack will die faster.