An argument for removing MP from the game

[Shurrikhan]

Is there any other class than BLM for which MP gates an optimal rotation? If not, then I agree MP should be removed from every class except BLM.

It doesn't bar anything rotationally, but MP does at least provide a granular measure of your (# of) remaining casts or abilities available on PLD and DRK, respectively.
So long as PLD's MP generation is not so stringent that every bit of MP must be conserved for Requiescat, then it cannot wholly be made redundant by Requiescat's duration alone (with Req being buffed and HS being nerfed, and both given at the same level, to show their new intended play).
Likewise, as DRK's MP costs encompass 3 spells, 2 very distinct from the last, it probably wouldn't quite do to force the interaction all onto timers and timer-trimming instead.

Additionally, it signals to healers that spamming AoE incessantly is probably not good play, and can at least feign that Cure, Benefic, and Physick are worth having on your bars (though I suppose one could consider that a demerit instead...).