immerseus is definitely easier on 25man no question about it and norushen is definitely the easiest fight for 10man but i've always thought mechanically and damage wise that immerseus is easier on 10man. protectors has a lot more mechanics to deal with and the damage output is much higher than immerseus. i did heroic progression in 10man so its just my opinion. some people can feel differently.
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it should be perfect. if a tank gets gouged after the first few attempts then they arent a very good tank. i am the He tank in my guild and i never get gouged. during progression i did for a few attempts until i learned that you cant just turn your back on heroic, you have to run a few yards away too. after i figured that out, never happened again. a taunt macro is still a good idea but it should be for RARE occasions, not every other pull.