7 Seconds of Stun equates to 3 global cool downs.

3 Global Cooldowns is roughly 25-30% of your MP. Pulling at 25-30% of your MP means somehow, in someway, with multiple ways of restoring MP, you ended the last pull at close to 0% and ran to pull the next pack near immediately.

-That isn't an issue with White Mages. That's an issue of poor planning and lack of foresight.-

The only time MP should be an issue is on a single target with Dark Arts spamming. Every other scenario your MP gain is positive, and this only increases further in AoE packs -even assuming wasting 7 seconds of Blood Price duration due to Holy Spam-.

PS- Holy Spam means the FULL DURATIOn of the stun isn't being applied. The Stun is applied when the DR duration is greater than the current duration. This means that you aren't even dealing with the full 7 seconds of stun; More realistically it's 5. (4s to 2s, 2s is reapplied, 1s applied, immune). 10s of Blood Price on a respectable AoE pack is full MP.

Period, end of story. MP Management is part of being a Dark Knight, and they have so many ways of getting it back, being in a position to be OOM because a White Mage went holy happy is entirely the Dark Knight's fault. There is no way around that.