Quote Originally Posted by KaivaC View Post
if they had a unique mechanic where, will in Grit, they get an additional passive defensive bonus, at the cost of their MP i.e their MP will take the damage before their health does.
So technically Dark Knight has this in an active version via TBN, gaining a defensive bonus in the form of a shield at the expense of about a quarter of your base MP. The drawback of making something like that passive is that it provides less engaging gameplay (or at least that's what their argument would be along the lines of).

That being said though, there is a game where this specific mechanic has actually been done: Aion. The Aethertech class has a buff mechanic that involves reducing their damage taken by a sizeable amount for an extended period of time while having half of the damage reduced by the effect dealt as MP damage in addition to a constant MP drain as long as the effect remains active. To offset this, the Aethertech comes with a wider array of abilities that generate MP. It's certainly something to look at for future tanks in this game I'd think.