You realize that PGL does comparable damage to every other class without activating a single MP drain stance right? You also realize that once it activates a stance it potentially blows every other DD out of the water when it comes to 1-1 DPS. Add to this the fact that it has skills that do recover enough MP to allow a PGL to sustain MP drained by a single buff.

The skills that drain MP on MNK will further increase MNK's utility in battle as well as DPS. Having so much more DPS comes with a cost - a stat you have to manage.

You see, your notion of MNK becoming weaker than any other DD class is based on absolutely nothing but conjecture. That will be based entirely on the magnitude of the buffs and how much DPS a MNK is able to put out with them active.

My estimation is, basing it off how potent PGL is at this time, that MNK will be very, very powerful - but will also be high maintenance. High cost = high reward.

You can continue to blindly whine about MNK requiring higher maintenance, but the fact remains at the end of the day whether or not the job is worthwhile will not depend on whether it uses MP or not. It will depend on if the power is worth the maintenance.