IMO level sync was a welcome addition to FFXI and its hardcore party requirements of needing a full PT after level 10 just to level and *needing* a bard or red mage past the mid 40's to get anywhere close to decent exp, it let you fill those gaps a little easier and actually get out and get some exp instead of sitting in jeuno for 8 hours straight hoping a RDM logs on between the levels of 50 and 52 (but not 53 because your whm is only 48 and he'll gimp the exp). It also made all of those level restricted BCNMs and Missions *much* easier for people to help out with and get done when they're above the cap for it.

Honestly, FFXIV is much more solo and small group friendly, and you can still progress on your own as any class while trying to get a PT together, so I don't really see a need for level sync for general leveling purposes. However, I really enjoyed the level capped Missions and BCNMs from FFXI and think bringing them back in tandem with level sync for them would be a great addition to the game.