Level doesn't affect much in the way of power or anything. It's mostly a means of determining what quests you're allowed to pick up, and what gear you're allowed to wear.

Yes, there is also the learning new skills part. But. Due to the Level Sync feature utilized in all instanced content, your level, including stats and skills, are squashed down to what is appropriate for any given duty.

The only thing you truly trivialize by being over leveled is general world trash mobs, which never really pose any sort of threat to begin with.

Further, your level by itself doesn't contribute very much to trivializing anything, as the majority of your stats come from gear. Keeping your gear at an appropriate zone level, rather than worrying about having the best possible for your level, will prevent the effect of trivializing zone content.

In short, exp level is more about content gating than it is about power level.