They had a good thing going when Endwalker trials gave busted EXP. No clue why they fixed it. Leveling felt sort of fun when you could just do fun fights to get nice exp.
All my jobs are 90 except the handful I got to 100 before burning out. I have viper at 80 with no motivation to level it further. Leveling a dps right now feels terrible. You either wait in a queue forever, or you do fates I guess. Oh, or go spam Aglaia, that place you've probably done a lot since it's been out for like 3 years.
My proposal: make side quests give a LOT more exp. Make FATEs mostly boss fight styled instead of trash mobs and increase the EXP gain from those as well. Make normal raid and trial roulette give meaningful exp again. Do the frontline thing, where you can queue up as one thing but play as another and have that exp transferred to the job you actually need exp on. I have a healer at cap. If I could queue that and play as that for the instant queue but put the exp on my rdm or something, I'd do it.
Leveling still wouldn't feel very fun under this system, but there'd at least be more avenues to get exp than just "spam highest dungeon" "spam aglaia" "run fates while watching a movie"