I didn't mean to sound snotty! I know that I would not have been comfortable on a group ride, if I was unsure of some of my skills. The rides I lead are FUN. There are social and recreational, at speeds of 13-16 mph. Sometimes there's a slower group. We stop for lunch and other things. We don't do pacelines (well, maybe lines, but not pacelines). I rode a lot with others in small groups (2-4) before I went on a group ride. That built up my confidence.
If "C" level is 18 mph, then I would be a C rider! While I certainly ride that speed on the flats for short amounts of time, my average is more like 14-16.