1. PvP gear is not restricted to PvP, it can be used in PvE.
2. i90 PvP gear has decent stats it just substitutes one stat for Morale. It is not useless for PvE, it just isnt the best. Same goes for PvE gear in PvP.
3. PvP gear without materia is still great. Nobody needs materia for their PvP gear. Perhaps in 6-12 months, but not now, and not soon.
4. I see no real economy happening from PvP gear as all of the equipment aside from the absolute worst tier is purchased with Marks, not crafted. This includes PvP matera
5. A full i90 PvE gear set is equivalent to a full i70 PvP set when used in PvP.

Bottomline: PvP does pretty much nothing to the global economy, and crafting (aside from melding) won't do jack crap for PvP. Unless you're using a fresh 50 alt job that you have no gear for in PvP, there is no reason to purchase craftable PvP gear.