It is viable to be end game without crafting. Mainly by supplying items for the crafted gear, while for your own gear you primarly use grand company gear from seals, then darklight and dungeon drops.

At end game, top end crafted gear requires both materia from spiriting bonding crafted gear, and special crafting items that can only be purchased through tomestones of philosophy, which you get from running level 50 content.

So some dungeon runners use philo tomes they get from running dungeons to buy crafting item, which they then turn around sell for gil, and some do spiriting bonding to sell materia. (Though this itself requires an investment in gear if you don't make the gear you are spirit bonding yourself) Spirit Bonding is a big income source for some because top tier crafted gear requires materia via forbidden meld which has a very low success rate. (You can go through a lot of materia before one finally affixes).