The 1.0 GLA class quests also had a battle where a npc enemy actually switched classes mid battle (he started out as GLA, but then switched suddenly to MRD, changing to a great axe from a sword and shield, supposedly to give himself an edge as his opponents weren't expecting it. He also tried the same trick against the player when they had to fight him as part of the quest - in both cases it didn't help him and he still got his lalafell butt handed to him ).

Also basic Conjury (specifically, healing spells like Cure and Esuna), is stated as being a core skill taught to many people as a form of first aid regardless of what Discipline they normally hold, particularly in Gridania where it regarded as being essential for survival in emergencies where a CNJ isn't always available.

Either way, it's clear there are numerous situations where npcs and enemies are shown either switching class or cross-classing abilities which are not their own (to say nothing of Rosenthal being both MRD and MSK at the same time even back in 1.0, clearly dual-wielding a great axe in one hand and a flintlock pistol in the other! But I digress...).