Well he got a point in that it essentially gives you another emergency timer. The relative value depends largely on the fight you're looking at, so overrating it is bad ofc. But for itself this is a powerful thing, a bit like a controllable Black Heart (though there's better ones for that).
Avoidance clickies are so/so. Mitigation/HP clickies can be powerful so they're big enough, since they give you another shot at surviving something which would otherwise kill you.
It's usually safe to assume that so your healers aren't asleep, the "normal" damage in a fight is healable. It's the stacked specials or bad moments which kills you, anyways.
-- (The Death of Rats, Terry Pratchett, Soul Music)