Yeah, the official statement is that the dungeons would be abused for incredibly easy experience (they are all super fast to speedrun), and thus there would be a lack of people in actual lvl 51-60 content.

Quote Originally Posted by GabrielK View Post
Still, they could allow them to give exp at least up until you reach 51.
New players get to 52 just by doing lvl 50 MSQ.
Old players on their first jobs will easily get to 51 with the Ishgard MSQ and side-quests.
Old players on their secondary jobs are the only possible issue, but with the Armory Bonus and NT Fate-zerg, it's also no problem.