I suppose there's a semi-valid argument that allowing tomestone lockouts per job would allow people to gear up faster than normal and throw off the curve (eg: If you're a White Mage main, you could use your weekly cap on the Seraph Cane and Orison gear, and then level up Astrologian or Scholar to buy your belt and accessories on a different cap).

But I can't see any possible reason whatsoever not to at least allow people to have a separate cap on "Tank" Tomestones that buy tank gear, "DPS" Tomestones that buy DPS gear, and "Healing" Tomestones that buy Healing gear - and it wouldn't really upset things to go a step further and have "VIT", "STR", "DEX", "INT", and "MND" Tomestones that buy gear for all classes that use each of those main stats.

The only reason to consolidate lockouts, in my mind, is if separating them would actually accelerate the gearing process for any particular job. The current system does nothing but discourage you from playing more than one job/role per character, when being able to do so should be one of the stronger features of the game. And as far as I can tell, there's no actual benefit, to the players or to the game as a whole, in limiting the weekly caps this way.