Mits and morale are important, but sacrificing too much mastery/crit will hurt infinitely more. If you can't be a menace to defilers/WLs, you're nothing more than a wet towel that can't be killed easily. Sometimes glass cannon is the better option, if you have good healers + LM for tar + depending on creep composition.
Healers can keep you up for a while with cd's. Once those are gone, there's less frequent heals (Bolster Courage animation), and you'll just get burst down with only 20k morale, if you have no mits and critd.