> Averaging 20 mph over non trivial distances puts you in elite territory. Most people can't sustain that, even experienced cyclists.

Probably. I've never owned a road bike so I was leaving room for the possibility that I don't know everything. (I have ridden thousands of kilometres per year in most of the last ~15 years, mostly urban or suburban, and I have considered myself fairly fit for most of those years. But who am I to tell what other people reach on lighter equipment?)