What classes could share gear with ninja?

[Seraphor]

Eh, just the point that it's not just simply DPS, it's physical ranged DPS. As such, it was only natural to dump it in with the other physical ranged jobs. In order to fit in with Ninja, I'd expect any job will have to fit the niche of "physical melee DPS."

You're not wrong from an aesthetic standpoint. But from a game code view, I'd expect it has to be this way. They designed Dancer as ranged, so it has to share ranged gear.

I doubt it has anything to do with the code.
Ninja uses aiming accessories, so there's overlap between the two roles in that sense already.

It's most likely a design choice, and respecting that people tend to 'main' roles, some main healer or tank, some main Physical Ranged DPS. So those phys ranged mains will want to be able to gear up all three phys ranged jobs at once.

Obviously melee DPS are a clear outlier here already, and an exception to that mindset, but that's precisely why they looked at adding a maiming job to share with DRG, and probably consider NIN to already be a bit of a hybrid due to the aiming accessories.