I would have to disagree with your overall assessment of 'early MTB history' based on your experience alone. Sounds like you ran into the kind of folks that are present in every sport, the ones who are trying to be something based on popularity or recognition or coolness.
I found the MTB racing community to be very welcoming and down to earth guys who were passionate about their sport, and worked hard to hone their skills and share their knowledge with those of us who were just getting started in 1987.
That course you rode in a park in flat Chicago was not an MTB course. It was a BMX course, set up for an introduction into mountain bikes, so it is not surprising you and the cruiser guy did well. It's interesting that they set it up for a 'race' format, and not just a chance for people to get on a MTB and try one.
While many successful MTB racers / riders ( the ones that were born after 1960 ) had their roots in BMX, there were many of us who started mountain biking in our 30's during the late '80s. It was hardly a 'soccer mom' (whatever that is?) mentality. We found a healthy alternative that provided a way to explore the often unreachable-by-foot limits of the outdoors and trails. And turned some winter only used trails ( downhill and cross country skiing) into year-round use trails that helped sustain and broaden the scope of many a ski area and other recreational land.
Sorry for the side topic nature of this comment, @metalchewy , I just felt another perspective was needed on the 'real history' of the MTB.
Remember, just because BMX came first, doesn't make it better, or more important.
