I have to agree with you that human can travel amazing differences on a bike. Even living in Holland you can surprise people by say you can travel 50km in two hours. I've also done cycling trips and figured out that you can average 10km/h over a whole day including all breaks for eating without even really trying.
But one thing I found interesting was that if you look up energy efficiency of travel for animals (in Joules per km) human are fairly average and eagles do the best. If you you include humans on a bike then we handily beat every other animal. Bikes are a very efficient form of transport.
The only reason modern bikes took so long to invent is that the materials for needed for the gears and chains (also needed for cars) just didn't exist.