One function of levels is to spread and pace content, and to guide you through it. If you have an epic tale spread across 1000 quests, you can make a game with 50 levels and have each award 5% of a level. The earlier parts will have simpler gameplay, the middle ones can transition to using skills more strategically, and hopefully you avoid making the ending “difficult” by pumping up the numbers.
Some players in The Lord of the Rings Online™ have been complaining about leveling too quickly. If you stack rested experience with recent bonuses and the new leveling curve, you move through some levels very quickly. If you want a quest to be challenging, you need to plan on hitting it soon, because you will outlevel it within the week, at which point it is green and gray content. Mowing through grays can get boring.
City of Heroes, however, lets you keep almost all the content challenging no matter what level you are. Content is instanced, and levels scale. If you missed a story arc, hit Ouroboros and flash back to it; set your level lower with Ouroboros to make non-instance content challenging for your (new) level. You can exemplar down to play with friends, and task forces do that automatically. In the other direction, you can sidekick up, and Mission Architect can be rigged to auto-sidekick everyone. There is very little you can do at level 5 that you cannot do at level 50, and almost none of it is interesting.
Farming, powerleveling? Unlike many games, it will not hurt your City of Heroes character or make you miss content. You can always go back and do it, without its being trivialized. You can skip the entire game, but that just means you have the entire game as a menu before you, rather than whatever 10% is available at your level. Higher levels mean more content options, not just different ones, and you do not lose the old options.
Once again, I wish more games would learn the lessons that City of Heroes has been teaching for five years.