Originally Posted by
Stepjam
While creatively, it isn't a bad idea, that would put DRK at a disadvantage in terms of damage. Many fights (particularly in Savage) have strats that involve actively using invulns, and with your idea, that would really hamper DRK's damage output as they'd have to "waste" MP on a non-DPS action. Even TBN is dps neutral when used properly since it essentially refunds the used MP.
If every single invuln had a damage reducing side effect, this might not be so bad, but since they don't, this change would hurt DRK more than their current invuln does. It's wonky, but at least with healers who are on top of things/a Whm with Bene, there's not too much to worry about.