Only MH fight that should drop you if you don't know what you are doing is Rage Winterchill's Death and Decay. It's a percentage damage effect, so same at 70 that it is at 90.

The only BT fight that may do the same is Mother Shahraz, if your characters are horrible and dont know the fights the Illidari Council may also be an issue (esp if you run in after Mother with all the cooldowns off). If you don't interrupt spells with your team that fight would be tough.