Yes, that's exactly what he's saying and he is 100% correct.
http://theincbear.com/agility-stamina-breakdown/
You go survivability because you need at least a 525k survivability cap so you don't get blown up by a bad RNG melee swing from heroic Nefarian. Even geared the way he is, Sejta is still below the recommended 525k survivability cap for Nefarian (he has 523k in his gear), and Rawr correctly shows this by suggesting he gem full stamina. Unless
you're tanking heroic Nefarian and need a 525k survival soft cap (highly doubtful), then you should go mitigation.
Seriously, run a simulator before shooting your mouth off, because you just look like a fool who's ignoring the theorycrafting.
Edit: Bheta, I plugged you into Rawr and it suggests enchanting armor on your back/gloves, and gemming agility/agility+stam/agility+dodge. This will decrease your total health by ~6k, but will also decrease the damage you take by ~500 per boss swing (assuming reg 10m Atramedes, which is what I assume you are progressing on at 6/12). Which means if the fight lasts longer than 12 seconds, you've already saved your healers a ton of mana and lowered their blood pressure substantially.