Level cap content can work just fine. Look at GW2. Sure, you might be a level 80 badass in town, but once you step into the world you get capped down to the highest allowable level for the region, making all content relevant, all the time. The only difference there is is that you have more abilities available to you, and cooler looking gear. If you want to take down that champion level boss though, you're still going to need a good number of other folks.