Like a lot of people are saying, new content (or lack thereof) is the real issue, not power leveling. Power leveling wouldn't feel as necessary if there was something fun and engaging to do, but as many have said, we've done all that already. It's not interesting anymore. You think being 50 with nothing to fight is boring? Being forced to level slowly through stuff I've done a hundred times already is boring and tedious, which is even worse.
I think the grind should be reduced and new content added (easier said than done, I know), but let's not forget originally this game, like all MMOs, was designed to deliberately waste our time so we would keep paying, but the monetization part is gone and all that's left is an old system that could be experimented with to try improving it so the game is more fun. We're all here because we like the game so the potential is there, but forced grinding is not a good way to keep us here. After all, it's a major reason why someone like me quit every other MMO I ever played and vowed never to play another. City of Heroes manages to be in a unique situation, making it an exception.
IMO, power leveling is also grinding, just faster than regular grinding, but still boring and tedious. I don't want to power level. I just want to play the game, tinker with builds, and fight bad guys without an endless abyss of empty bars that fill exceedingly slowly in my way.
Also, a sad, but simple truth is that there will always be some portion of the player base that blows through content quickly. It happens. You cannot stop that. It's futile. But it isn't fair to the rest of us to design the game solely based on the needs of the first to finish.