There already was an incarnation of Subjobs back in ARR/2.0. Some jobs got minimal from it (PLD got Stoneskin and like 2 other useful abilities), some got MAJOR pieces of their role (WAR and DRK required GLA22 I think it was for Provoke). All melee dps had LNC for Blood for Blood, all ranged(MCH/BLM/SMN) had ARC for Quelling Strikes. (I didn't list everything, but this is what I remember off the top of my head)

No, the original Subjobs weren't anything like XI's iteration of them, but they still were Subjobs.