Other than potentially "losing" exp on a capped out class, there's no real downside to being overleveled. Stats are tied to gear, and you won't be using most of your skills before they are needed because A:Most of the important fights are instanced and get level synced and B:Many of your most important job skills are tied to quests, which you won't be able to access early generally speaking.

It's annoying, but it's better than being exp starved IMO. I think they set the exp knowing that a lot of players will want to push through MSQ to the end without needing to stop and grind. When you are at "current", the exp gain is more "normal" when you enter an expansion at launch.