Unironically all of the pieces are there, they just need to apply them properly.

-Regular dogshit 4-man dungeons? Replace literally, and I mean /literally/ every single one of them with a Variant Dungeon equivalent. The same 2-boss run(unless you guys specifically do a route with 3 bosses) that has the same guided NPC path that gives you slightly more loot if you follow them. You'll be incentivized to do a little interaction to see which path you want to go down, but then make it quicker to clear and provide rewards for hitting every single one so that it's not mind-numbingly wasting your time like present Variant Dungeons. You can even combine present dungeon series into Variant Dungeons.

-Revamp all fields in all zones into being closer to Field Operation zones, with specific unique FATEs and regional superbosses being poppable through farming specific field enemies and grant appropriate rewards for clears and certain setbacks for failure to clear. You can also include Pomanders as regular items to use in the field to modify your time out on the road. Inccreased enemy spawns? Specific enemy spawns? Treasures that Treasure Maps can't find on their own? Petrifying the whole map at once? All fair game.

-Bring back Job Identity by using all of those Job-specific skills inside of PvP and integrating those special skills inside of Field Operation areas into subjobs or some kind of mix-and-match tray you can devote a hotbar to. You can also just take the general 1-2-3 skills and put them into one single slot so you can fit more varied actions in their place, as well as making subclasses simply swap out specific skills in order to reduce button bloat and instead increase variance in each button on your hotbar.

-Give MIN and BTN a Deep Sea Fishing equivalent

-Make Frontline a 1v1 faction mode or make Rival Wings an option for PvP Duty Roulette

-Increase the number of games in Gold Saucer and the amount of ways to earn MGP

There, entire fucking game fixed.