I suppose it comes down to whether you think the reduced enmity and extra few HP healed is worth that extra ~40MP. In some fights where enmity is a bit wobbly I am sure it will be valuable, but I think Cure V deserves a lot more, being as it is one of our signature spells. I think it should be objectively better on most/all fronts. Sorting out the MP efficiency would do this and let it function even better as our flip/flop IV/V pair of heavy duty healing spells.

The only reason I am so keen on sorting out MP cost for Cure VI is that I can't think of a suitable secondary effect that could possibly make the spell worth that sort of cost. Even if a suitable effect is found - removing multiple status effects or something - you've then got to find a situation in which you simultaneously need both obnoxiously expensive high potency healing and the full effect of the secondary function, or your efficiency goes down the toilet; you will also end up with people using Cure VI only for the secondary effect, and that kind of wastefulness does not sit well with me.