Way too much emphasis on the "MT" role for current content.
As an example: Sarth: The OT tanking adds is really important as well.
KT: The OTs tanking the adds are really important as well, possibly more so than the MT.
Faerlina: OT is important again here and taking a ton of magic damage while holding aggro on 4 mobs.
Patchwerk: OTs take more damage than the MT.
Gothik: It's really 2 MTs on this fight if you think about it.
4 Hmen: 2 MTs again.
The old concept of MT / OT has, to some extent, fallen by the wayside now. While being MT could be a symbol of prestige, I wouldn't be totally fussed by whether you're picked as MT or OT, so long as you get to raid. From experience, if you prove you're dependable over time, you will get your chance to MT.