Bug or feature?
Many games with expansion packs have started speeding their players to the end, so that they can be where all the other players are (and need to buy the expansion pack to advance). WoW does this most visibly, even before having you invite friends for triple xp and zebra love. The Lord of the Rings Online™ made the early levels faster and started running nigh-continuous bonus xp weekends, weeks, and months.
City of Heroes may have done this with Mission Architect. Farming is more or less constant. You can pick the enemy best optimized for your character or make your own perfect foe. Grab friends, smash, repeat. A single run through a good farm will get you to level 20. This differs from normal powerleveling because Architect can be set up to auto-sidekick everyone to the same level range. You no longer need bridges, care in mission selection, or anything: pick your ideal enemy, fill a mission with copies of that one guy, and smash. If that is too hard, add pets that will increase your defenses.
City of Heroes, however, has no endgame. There are a few hard things to do at 50, but mostly you can just keep running missions. A variety of tools let you do pretty much anything at 50 that you could earlier, so it is always better to be higher level, but it is not as though you are raiding or something. Getting to 50 means being 50, maybe farming for those purples.
City of Heroes is, however again, very alt-friendly, complete with sales of extra character slots of more alts. Want to try a new character? Bam, level 20 in an hour, try a dozen new powers. Out of character slots? Bam, $20, 5 more. If people are racing to the level cap and re-rolling, that can only mean more money. Or they quit, but your most competent power-levelers are long-term players who came to peace with the lack of endgame years ago.