I think if you stand back and just take a look at the concepts behind the subjob and combat systems of FFXI, you will "get it". If you never played a MMO older than WoW, then you will probably never "get it" unfortunately. I'm sure the devs could easily find a way to create that level of flavor in FF14 in a more contemporary way - they are exceptionally talented after all.
How do you describe a job in FFXI.....?
1. Weapon skills each with its own weapon abilities.
2. Active job abilities unlocked according to level
3. Passive job traits unlocked according to level
4. Magic skills with spells acquired through quests, drops, npc merchants and the player auction house
5. Level based stat bonuses
How do you describe a job/class in FFXIV?
1. A single weapon
2. Active abilities unlocked according to level (conceptually includes both spells and weapon abilities)
3. Passive traits unlocked according to level (job abilities do require a quest to complete)
So... not only are jobs in FFXI more inherently more complicated and interesting, but the sub job system added another level of interest. Would you take a subjob for the stat bonuses? What about the abilities or spells? Yes, there were combos designated as "required" by the community, but balance is always a thing with MMOs.
Things that made FFXI combat interesting (once again, ignore the pacing)....
1. Resistance play - not every mob or encounter would simply be nuked or cc'd with the same ability rotation. You would have to be smart about weapon abilities with elemental damage.
2. Crowd Control - encounters were designed to heavily encourage the use of crowd control. Here, while we have CC, its use is negligible.
