now i will preface this by saying yes you can learn most of the stuff taught here online in the balance discord, youtube etc.. but the point is more so that you have somewhere to actually learn/practice these things and get stuff down to muscle memory in game.
what i propose is since people do struggle with jobs and mechanics of said jobs these new halls would be more job specific (with the potential for more role generic halls if needed)
available at 50 (advanced) and current expansions max level (expert) (would change depending on expansion of course so for example hall of experts would be changed to accommodate the level 100 changes which shouldn't be alot of change unless they change alot of the stuff taught or add new abilities that change how these things interact with eachother)
a few examples of things gone over.
for example disengaging and reengaging as a melee DPS using your gap closers/disengagers. take for example being taught as a DRG to use your elusive jump to disengage from the enemy who's casting a melee range AOE. so you'd see him start to cast you GCD elusive jump his cast finished as you exit elusive jump animation then you spinehsatter dive to hit your next GCD learning how to diminish downtime(of course this could also just be an overall melee DPS thing excluding i believe MNK possibly he would just move out and reengage i think)
and for the expert training you could teach DRGs about the double life of the dragon window
for ASTs you could teach card targeting simple (basically melee cards go to melee ranged cards go to ranged) and how to use your divination with the parties buff window
expert would teach you stuff like preplanning your earthly star and more complex card targeting (it'll show you that every 5seconds the MNK has a burst window and the NIN will have his burst every minute. so you want to play the card on MNK cause he will get more use out of the buff at that time. but at the minute mark NIN has bigger burst damage, so at that minute mark you need to have a card for his burst as well or you won't meet the DPS check for clearing that part)
of course i'm not an expert myself in every single job and know all the little nuance/tricks every job has but it would be nice to have more ways for people to practice/learn these things without needing outside resources
i would also have a portal appear beside the quest giver for the ending level 50 quest for each job. alongside being accessible from the novice hall NPC. the portal to the expert halls would appear near the role quest givers alongside of course being accessible from the novice hall NPC
also yes ik alot of people didn't use the novice hall, but thats not a reason to not attempt to give players that want to get better the resources necessary to do so. like for example alot of people want a more interactive SSS that throws mechanics out for you to dodge while doing your training