If you also play ranged jobs, then the accessories on those overlap on Ninja.

DRG had to have different gear in the past because they wanted it to have higher physical defense because at one point in time it was supposed to be a more physically tanky sort of frontline DPS when they had ironed out some of the kinks of why that's a bad idea yet.

It let you do fun stuff like eat a Sephirot Ex tower on DRG instead of tank and save the party from a wipe with your 80% +parry cooldown on a 40 second timer.

If anything, I kind of wish they hadn't veered away from what they did with Ninja originally on its introduction. This was that all of the striking gear up to i110 was shared by Monk and Ninja, and it made a lot of sense to me, because they both had high attack speed due to intrinsic buffs (GL and Huton). They merely added DEX to the striking gear.

I guess they had Ninja splinter off, so that Monk wouldn't have to compete on raid drops, but with the way raid drops work now... almost nothing matters in that regard.