Level sync UP enemies not players down.

[Drkdays]

Level sync is one of FF14's greatest charms. It keep the game from stagnating and reminds players of the challenges they once faced and new players or old players with new classes have to go through.
Plus it's a great way to learn more about your early abilities.

Furthermore, if all dungeons matched your level it would become tremendously tiring to constantly fight enemies of the hardest difficulty. Note also that this is basically what WoW did in poor imitation of FF: max lv players providing significantly less dps than a low lv player with better synced stats.

Syncing down may make you feel weaker and more awkward, but that's an illusion. If you're synced down your ilv is always max for that particular dungeon so you are actually very strong.