I honestly think that they should remove the classes and the cross-class system altogether and replace the 5 cross-class slots we have with 5 new job-specific skills that replace them and add some new effects specific to the job. Like instead of every physical DPS ever cross-classing Lancer for B4B and Invigorate, make them all have their specific TP-recovery tool which could work a bit differently for each job, and make them get their own temporary damage buff instead of B4B which would also have its own mechanic depending on the job (Like for example MNK could get a 3min CD buff which would instantly grant them GL5 or GL6 instead of GL3 for a short amount of time, boosting both their damage and attackspeed even further at the cost of HP just like BLM's Convert, and the GL5-6 wouldn't be refresh-able, forcing to go into a Perfect Balance rotation afterwards to get back to GL3 fast and giving an opportunity to actually use Tornado Kick within a burst rotation since you could use it right at the end of this new buff, NINs could get a Kage Bunshin sorta thing which would mirror the real NIN for a short amount of time but with only 30% of its damage - Just some ideas which came to my mind as I'm writing). It would be the same for tanks, each would have their own taunting ability, an equivalent to Convalescence and Bloodbath in terms of survivability, etc... But with different mechanics which would follow the general idea of the job (Warrior being an unrelenting wrecking ball of meat and steel, Dark Knight being an intimidating edgy edgelord soul-thirsty slayer of death who can summon a black hole inside your body while cutting you in half, and Paladin being a shiny white knight spreading light upon the whole country while protecting everyone with very shieldy shield skills and wielding some white-magic powers).
But that's a whole other thread lol