I wasn't trying to dismiss that the key being a +5 made it okay to leave the key, more the fact that the healer thought that they couldn't finish based on the damage the tank took, had the healer pressed more buttons I'm sure they would've been able to finish even with less than a competent tank. Hell you could probably have a warlock pet tank bosses and trash.
My general thought process was also more close to : I'd rather not they implemented a punishment system for what happens in small keys (sub 15s) that would cover all key levels.