Well question is did you MT with that toon? Or did you use it together with a properly geared tank? Because it's my experience that besides 1 MT it only requires one plate class to be around. I've solo tanked marrowgar with the 10% buff in 10m normal mode, with a dps dk standing next to me.

My point being that a very poor geared tank (quest greens/blues) has probably more avoidance and an equal amount of health than a very well geared plate dps class. So in the end that doesn't seem to matter a lot as long as your MT has decent gear.

Of course this is still a very nice & fun achievement.