We need the jobs to be easy to start, but difficult to master. The jobs have to be fun and bring something to the table, regardless of the level of difficulty the content has. So, not just Ultimates are allowed to be "Fun".
We need the Trinity to be resurrected. Tanks need to tank, Healers need to heal, and DPS need to DPS. The game needs to be more than an easy-to-plan Dance Dance Revolution-type of content.
We need more interesting ways we approach content. Like Blue Mage, Summoner and Dark Knight were in FFXI, where you needed to go out into the world and interact with other aspects of the game. Granted, they don't need to be as annoying as killing 100 mobs with a, what was it, level 1 sword? But something like BLU getting their spells from overworld mobs, then going into dungeons and having fun with content.
We need more RPG elements to interact with the world.
For example, the overworld mobs are cool, but what if you could just go to a map, and during a full moon, you could fall into a solo dungeon? This could incentivise exploration. What if certain Jobs could find these dungeons easier? Something like the zone itself would be easier to navigate and find these secrets if you are a particular Job. Like in Garlemald, an RPR would have a better time exploring, while in Doma, a NIN would have the advantage.
What if doing certain EX trials would give SMNs a catalogue of Eikons to choose from, having them be reskins of the usual 3, but with different-looking spells (even if they function the same)? Like, imagine instead of Garuda, I can summon Ravana and have Ravana-themed spells?

The jobs also need to be more fun to play, specifically, play into their fantasy. We need something more interesting than Blue, Red and Green DPS. A WHM should have abilities derived from the elements, like stoneskin and their PvP ability of turning people into frogs. SCH need more DoTs and play into the tachtician role! Less heals and more shields, Eos should be the pet healing turret. DRK should have more mana and health management playing into the dark/death vigilante, who fights to the end for what is right. etc.

We need to demolish the homogenisation and let the min/maxers cry about it. There should be fights; certain jobs would be worse to play than others. They CAN get away with that, by the virtue of 1 character being able to play every job, one sucks in this content? Try another.
We should have more fun things to do, PvP is right now the place majority of Job fantasy resides, and I don't know how long that will be. Like seriously, let me pull every mob and polymorph it with a WHM! Let me yank mobs with WAR. Let me draw a fat chocobo who is bum-smacking the boss with a Picto. And so far and so on...

Wow, I went on a rant. But seriously, right now, the hardest part of playing any job is the fight to stay awake during content. Also, fix the scale and let us bring all of our new spells into older content. Just recalculate the potencies.