As someone who usually plays more in off-peak times, I get the Trust argument and wouldn't even complain if their AI/output was improved to be better in line with real players. I also agree that ability syncing should be a thing, too.

More specific to the leveling queue, though, I'd say to implement a system we could simply call Treasure Sync with some additional perks:
1) Any treasure chests prior to the first boss in a dungeon are removed. These typically contain garbage loot, anyway.
2) When a chest is opened, every player in the party receives an item. No longer is there a lot process.
3) The item drawn in #2 is tailored to both your level and class. As an example, if you're a level 68 Paladin, if a piece of gear rolls, it will be appropriate for a level 68 PLD even if the dungeon you're currently in is Satasha.
4) In the event of acquiring unwanted gear, turning them in at your GC can also reward a small amount of experience. Players at 80 can receive tomestones instead.
5) Add a unique currency to the Leveling Roulette that is acquired each time you use it and complete the duty. Said currency can be exchanged for materia of all tiers, tomestones, dungeon specific gear, and potentially new mounts/minions. The Mog Tome system could even be co-opted for this process with event times just yielding bonus tomes.
6) Greatly improve EXP payout if you happen to draw a Primal duty. Further reward a totem or craft materials upon completion if applicable.
7) Increase the EXP reward to 3 times per day instead of first-time only.

Ultimately, you can't really get around the population gradually growing more top-heavy even if we are able to level everything on one character. Unsynced runs are a hard out alternative for people who might just want to get a piece of story out of the way, but for drawing those who don't need the content themselves, you still need some sort of perk.