Guildleves made terrible players ^^ if they add level sync now they can ensure that all content is balanced for it and future content made with it in mind to stop exploits like Astral Burning in FFXI. Also FFXIV will not have the problems that FFXI had of players with weapons not capped as that system does not exsist in FFXIV
Now SE fixed that. Now the exp/sp you get on leve is so low that didn't worth wasting time on that, unless you need marks or some gil.