Maining a job in FF14 is more about learning the particular ins and outs of the unique elements in a job's tool kit. Most jobs within a specific role share a lot of elements so it's mostly about knowing what makes each job unique in whatever particular content you're going to be doing. The actual gearing part once you're at level cap mostly takes care of itself because most jobs within a specific role share gear outside of their weapon, and in most cases you're not even going to need to slot different materia.

So, yeah, gear takes care of itself and it's really about learning how to play the specific jobs, and that can be tough to maintain if you're constantly shifting around. Most players at end game end up "maining" a role rather than a specific job, or they'll pick one job for each role to avoid confusion on specific rotations, skills, etc.