All the drk math only works out if every single shield breaks and you choose to never burst for openers, in which a drk will blow its entire mp pool (unless criticals busters come up) And even then the drk will have to choose to not burst prep for the next burst window and only use its mp to shield and remain around 0-3000mp. Which comes down to mitigating autos, you will get some wild looks for doing that.

And as said above shields are not heals, shields falls off if their not used.

In a vacuum the math could maybe check out, but these scenarios wont happen.