I basically already did that going into Stormblood, went from a Tank (WAR, then DRK) to melee DPS (NIN, then SAM). Coincided nicely with Tsiron getting their ass beat by Zenos, story-wise...! I've since leveled WHM, BLM and RDM too, and while I could see myself playing RDM, "canonically" they're a "samurai" now.

My alt is, at this point (was a DRG originally), supposed to be the RDM main, but I've got one of each role maxed out regardless because Road to 70 made it super easy