I don't think this game lends itself to the ability of maining multiple jobs. Due to caps on tomestones/lockouts, I can't equally gear all of my jobs or even more than 1 really. This has eased with allowing healers to share gear, but even then the weapon is gated.

Personally, I consider a main job as the one you focus your gearing on and use for harder content.

For me, that is SCH. Second would be SMN which is sitting 11 ilvls lower than SCH atm.