NO to Level Sync...

In FFXI you did not have a viable way to exp outside a party...if FFXIV you do. You can solo leves for VERY good exp/rewards per hour.
Level sync just messes up the partying process by:
1. Eating up beginner party camps by allowing people to stay in the same spot WAY longer than they naturally should. All the party needs to do is keep inviting someone who is that rank for that camp and syncing to there level.
2. Doesn't allow people to progress in their class and learn the job/class naturally. Nor do they start using/equiping their abilities as the level since they can't use them.. if you think powerleveling creates poor players this just kicks it up a notch.
3. Makes buying better gear as you rank completely null and void. This already is happening to some extent now with how quickly people can level but it would just become crazy if syncing happened
4. Exp is currently stupid-easy to get. Quite frankly, if you are not smart enough to figure out how to do it, maybe you shouldn't be playing. (Leves 40+ you get 10K+ each leve complete...and in a SB/exp rank 45+ party you can get ranks 45-50 in under 2 hours...which I think is appalling but that's a whole different issue. )
5. Puts WHM's/Healers in a 'Premium Position' again where they can charge rates, or get bullied into constantly helping Level-sync parties. Most people who want level sync atm want it because 'healers are hard to find'. This is not due to the exp system but poor class/job balancing. SE already stated that the next class set to come out will include another Mage Class...this might help to alleviate some of the sh/ level 35-40 exp group 7/8 need Healer shouts you see in town.

A compromise could be something like the sprout cap in ffxi. It was a rare/ex item you got if you used a buddy pass/bought a world pass for a friend to play with you. If both of you put it on, it would drop you to the level of the new person for 30 minutes (you could re-equip and do again as often as you liked). This allowed you to party together and help your friend. This is maybe the only time I think level-sync is okay...when you are trying to help friends. And I'm sure they could create and item/quest that gave an item that allowed you to help ls mates/friends list people etc. But a blanket Level-sync NO THANKS.

Battle leves=level sync...use them.