Spin classes are legit. They're also great.

I'm not a speedy rider, but I'm fast enough that it's tough for me to ride with any recreational (non-racing) riders or even the several "B" rides in the area without ending up either solo or with only one guy riding with me as the pace is usually too slow. This became sort of a bummer in a triathlon training group that I was with for a few years, as I was friends with a lot of folks there but couldn't bike with any of them due to the speed differential.

In a spin class though, it's all good. I can hammer as hard as I want, and I can still get teh camaraderie of training hard with all the folks, both beginner or expert. It's also great because the instructor quality doesn't really matter once you're ready to hammer - whenever they say 'go hard!' you just push the pace as hard as you want. In times where it was dark out and I was time crunched, I've done AM spin classes where most of the folks there were retired folks barely moving the pedals, but I was happily making a sweat puddle in the back corner.