I really don't want this to devolve into chest-pounding, but I have worked in the bike industry, and have raced on-and-off as an amateur in road, cyclocross, MT

I really don't want this to devolve into chest-pounding, but I have worked in the bike industry, and have raced on-and-off as an amateur in road, cyclocross, MTB, and duathlon dating back to the late 80s. I remember when the Ritchey P23 was the state-of-the-art in lightweight mountain biking, something I chuckled at when riding a 17 pound carbon Ibis a couple of decades later. Wind resistance absolutely matters in every discipline of cycling, and you don't need to have been fooling around with bikes for forty years to know that. If it didn't matter, what are all those triathletes and time trialists doing with aero bars, flat backs, and disc wheels? It matters in MTB as well. The optimal position for efficiently generating power on a bicycle is actually quite upright, you can see this if you look at pictures of people riding "roller races," they usually flipped their handlebars up so they could be much more upright than when riding on a track. XC MTBs have much lower bars than would be most efficient on rollers without wind resistance, and that's because the lower position generates less drag, knobby tires and all. Even if you aren't riding a time trial or racing XC on an MTB, knowing where to expend your energy and where to save it matters greatly. If your daily commute involves hills, you will work less and arrive sooner if you don't try to crank your max while descending, and save your efforts for climbing. That's just math and physics. --- Also, please, I'm not upset at any random internet person using insulting language, but it is not constructive for our community to go around suggesting other users are "functionally illiterate."