Tbh, it doesn't matter if they asked him to stop. They were wrong. The only reason to try to keep targets slept is if the healer is bad. So the healer can break it if he wants. A ta no should never need sleep. Tanks should learn how to tank. Plus, casting sleep lowers dps.
Sounds like that party needed to be educated on maximizing dps.
The goal is to get out as fast as possible, not baby the tank.
Inb4 "tanking is hard"
I am a PLD main, the worst at AOE, a DRG "alt", and a WHM sometimes.