Both the 46-49 deadzone in ARR and the mid-50s "oh my god I hate Moogles" span in HW are spots where FFXIV's MSQ did basically abandon players to go grind for a while. They've been more or less spackled over at this point by XP buffs and alternate XP routes (PotD is great now but let us not forget that Challenge Log exp stopped scaling at 50; there's no indicator yet that PotD XP is going to scale on Stormblood launch and so it may end up being relatively useless if the XP curve post-60 stays up), but XIV definitely has fallen prone to the "screw you, level grind" issue before. It wouldn't be super surprising to see one pop up in Stormblood, too; a lot hinges on how they pace dungeon experience, since part of the problem at HW launch was dungeons providing relatively little XP, but at HW launch it would get pretty depressing to finish off the MSQ available and realize you needed to generate millions of XP before you could progress further because they stuck totally arbitrary deadzones in the leveling experience that served no purpose.
XP gaps aside, the Heavensward leveling tick/tock of new job skills alternating with new dungeons was a pretty good way to make every level feel meaningful (unless your job skill was garbage, hi Rend Mind)l, so it'd be nice to see them stick with that.