I wanted to get an opinion on what you all think when it comes to choosing specs in a 10 man team. Here is my exact dilemma.
I have a mage and a warrior in my group. Now we all know the better spec dps wise is fire/arms. However arcane provides 3% increased damage buff and fury brings the crit buff. I have no other classes that can bring these buffs.
Depends on fight I guess. Single target arms and fury is comparable enough that 5% buff is worth it but for fights like Yor Sahj heroic bladestorm is just too awesome sauce to pass up for downing those adds. Arcane is good for some fights but movement does hurt it. In a boss like Ultrax the buff will give more than the DPS loss to mage if any DPS loss at all. On fights like zon'ozz and yor I'm not sure but fire seems better. Thing is arcane is better on fights like hagara and spine anyway even wihtout the buff so it kind of depends what you're progressing on. Once something's on farm then you should be able to still down it using a qworse spec for it and use optimal spec for what you're struggling on.
Raid comp is pretty important during progression, but after play what they enjoy because it gets a lot easier. For example you ever wipe on a boss below 3%, I am sure most of us have. Having a ret pally or arcane mage means that would have been a kill. Now if your mage can do 3% more of the overall damage in fire vs as arcane then fair enough you don't have to switch. It is unlikely that would be the case though. So try to get a raid comp that has the majority if not all of the buffs and have that poor mage switch back to fire after the kill is ironed out. Sadly blizzards idea of bring the player not the class really lacks when it comes to 3% extra damage from ret/arcane and the spell power buff from ele shamans/demo locks.
Its alot more dps than you think. For examply if your raids dps is around 240k on ultraxxion heroic. 3% of that is the arcane mage's buff... 7k. So the arcane mage would have to do 7k+ dps as fire which means he is either
1. Really bad at arcane
2. Is "faking" badness at it just so he can go fire
Both of these are bad, becuase to refuse to min-max a better spec for the raid is to lose 5-7k dps for the raid, and the worst part is most raid leaders can't tell.
Now, the mage buff is easier to tell the difference between 5% crit, 5% spell haste, 5% melee haste and so on. Expecially when these crit/haste/spellpower differences also apply to the healers as well, its insanely hard to model what would be better just becuase it all has to do with your specific raid comp and how people do things.
My guild is 4/8H and honestly we dick around so much that we don't even think we are playing to that level, but we are anal-retentive about our raid comp and I think it goes far that everyone is willing to min-max offspecs just for a better raid comp and have 4-5 people who can heal depending on which classes do better. But the top guilds on our server have horribad raid comps with only like half the buffs but they are all so amazing at thier respective specs that it doesn't really matter. (ie, 2 rogues 2 warriors, 2 priest healers, 4 druids, etc)
So just test it out and tell people that this could mean the difference between wiping and progressing. Deciding whether they are just being lazy or its really just better off without the buff is a hard decision and things will go way better if people are genuinely invested in doing whatever it takes to better the guild.