The only end I can realistically see to this problem that SE would do is just to nerf the fates in N. Than for people level 51+. It seems... incredibly accidental that fate grinding in N. Than is still better exp from 50-55 than other methods of leveling (though most reasonable people I know end up doing those other methods because fate grinds are so soulcrushingly boring). SE could totally scale the exp in the new zones to fit better with N. Than's exp... but we know from experience that they tend to prefer buffing other, less mindless methods of leveling (read: dungeons), compared to the fate grinds. Additionally I think they really, really, never thought about people leveling waaaaayyyy faster than expected by going back to the original bane of FFXIV ARR's leveling system: FATE grinds. Not to mention I think that fate grinding is worse than it was before because at lvl 50 normally the amount of experience you'd get from the individual fate mobs would be a pretty significant portion of your total exp, but currently you can only hit a couple once before they die so you don't get exp from individual mobs much.

In any case, if you do your high and low dungeon roulettes and your trials roulette, then grind your highest dungeon, and also do the daily/weekly hunts while queued, you can level 50-60 in a couple days and as a bonus have a full stock of seals to start upgrading your armour as a bonus (which helps you to avoid the cesspool that are currently hunt trains, which are even worse than fate trains).