On the one hand, I agree that Black Mages have severe MP efficiency issues. Even considering the MP options opened up to Black Mages by the availability of Convert and Refresh from /RDM, or Dark Arts, Sublimation, and /SCH stratagems, the disconnect between BLM play in Abyssea and BLM play outside of Abyssea (especially when fighting mobs on which Aspir and Aspir II are ineffective) is pretty huge. Even with latent Refresh from my earring and body pieces, I find myself running out of MP fairly consistently.

That said, BLM's primary role in many outside-Abyssea fights is not to do damage, but rather, to do "crowd control" activities and TP move / damaging spell mitigation with Stun. Some people like this, some people don't, but I'm not sure that this is actually pinned to MP issues - a casting BLM can't sleep or stun effectively, either. Black Mage's damage-effectiveness as compared to the heavy melee DDs outside of Abyssea is contingent on timing and luck (magic burst, spikes of enmity, spell resistance), although this is less the case now with the cap at 90 rather than 75.

Personally, I'd be inclined to suggest a FFXIV option here, although I'm not sure how feasible it would be - change Aspir and Aspir II such that they return MP even from monsters which do not have MP to drain. I've noticed in play that playing BLM against Aspir-able mobs (with Aspir II in the picture) is a completely different ballgame than playing it against things with no MP, and the ability to siphon MP from any monster was something I greatly enjoyed about XIV's MP mechanics.