Class/Job Suggestion For a Tank

[Xathoa]

Well, it's commonly known that there aren't many tanks or healers. When going to do a dungeon, lone tanks and healers are more commonly going to get in quicker than a DPS class ever will. That's known.
We have three healer-types in game, including the jobs (Conjurer [class], White Mage [job], and Scholar [job]). We have four tank-types (Marauder [class], Gladiator [class], Warrior [job], Paladin [job]). And then we have a total of ten DPS-types in the game (Lancer [class], Pugilist [class], Archer [class], Thaumaturge [class], Arcanist [class], Dragoon [job], Monk [job], Monk [job], Black Mage [job], Summoner[job]). And that's not including the rogue and the ninja coming to be implemented.

And to add, we really only have three Discipline of Magic classes. I'm ignoring the jobs, since they still work on the base three classes.
With that in mind, we have five base Discipline of War classes (with the Rogue on its way, making a sixth).

So, what if we had another Discipline of Magic? And what if it were a tank? Just to up the numbers on the scale for the ones being outnumbered.
It sounds strange, but think of it like this- It would use robes like all Discipline of Magic classes do (which means an over-all lower defense [and hopefully means more robes in the makings for those that need better armor]), but it would use its Magic bar as temporary HP to make up for the lower defense.

I dabbled with ideas, and thought maybe it could use a Scythe as a base weapon.
TP would be used for a few martial/magical-melee abilities, especially to draw aggro, while some of the stronger abilities would use MP- but of course, that would be at the cost of your Temporary HP. So you'd want to use it wisely.
You'd have to activate a buff to use the MP as a temporary HP- so it wouldn't always be an active Temporary HP- allowing for it to regen normally when the buff is gone. The buff, of course would be on a timer. Maybe 60 seconds for the buff to last before you need to cast it again. And maybe a 30-second cool down for the temporary MP as HP buff. Since the class will mainly be using that as a means of defense.
This Magic-Tank will be using an auto attack, since scythes can be melee weapons. But they're very similar to staves as well, so they cast magic too.

It'd be something of a spell-sword I guess. But with an emphasis on Tanking, since Tanks are needed.
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So, what do you all think?
Anything you like or dislike about it?
Anything you'd want to change if it were a thing?
Would you play it?
Is there something wrong with the idea?