There are different ways to go about pentamelds as far as money goes. For example, fending acc melded with strength are, on my server at least, about half as expensive as slaying acc melded with vit, because the former is less optimal by like, single digit margins, but still better than any combination of i210 fending/slaying.

The str/vit problem could be easily solved in a way that doesn't screw with enmity or your gear by simply removing STR from all fending gear, and giving tanks a "cleric stance" that swaps the two stats, independent of their tanking/DPS stances. But this is such an obvious solution that for Squenix to not have done it by now means its probably not in the cards.