Across the spectrum, from the most utilitarian to the most high-performing, the range of bicycle designs is a continuum of subtle differences. As much as we like to categorize bikes, when we line them up, it jumps out that it’s actually a small series of steps that takes us from one end to the other. I attempted to illustrate this with the above graphic (click the “zoom” button).
Starting on the left is a carbon lowracer recumbent, and on the far right is a carbon time trial bike. In the middle we have a beach cruiser and a city bike. The lowracer and the time trial bike give up everything in user-friendliness to gain the most in performance. The beach cruiser and city bike give up everything in performance to gain the most in user-friendliness. The bikes between the two extremes are bundles of conflicting priorities, each making compromises to reach a middle ground between utility and performance.
There’s more to performance than aerodynamics, but reducing wind resistance is by far the most dramatic way to increase efficiency (at 20 mph, wind resistance makes up approximately 90% of total resistance). The cyclist’s torso generates a tremendous amount of wind resistance, so for maximum efficiency the body needs to be laid down inline with the direction of travel. But doing so dramatically reduces a bike’s user-friendliness because an upright torso position (with the rider’s feet near the ground) is the most natural and confidence-inspiring. Recumbents with high bottom brackets, and upright racing bikes with extremely low handlebars, both put the rider in positions that, while being highly efficient, are unnatural and limited in their practicality. And, of course, bikes that place the rider in an upright position, while providing excellent user-friendliness, are limited in their efficiency. (Fairings bend the rules by allowing an upright seating position with good aerodynamics, but they increase complexity, weight, and cost, thus reducing practicality.)
No particular type of bicycle is necessarily better or worse than another (though an argument can be made that it may be prudent to focus on practicality over sport at this particular juncture, but I digress). Each attempts to fill a need; the trick is finding the type that best fits an intended use. Bikes that fall in the middle ground between pure performance and pure user-friendliness (like hybrids and low-end MTBs) are popular because they’re versatile (and consequently, relatively inexpensive). But like other “all-purpose” tools, they tend to do a lot of things reasonably well, but very few things exceptionally well. So pick your medicine: lots of performance, lots of utility, or a little of both. When it comes to bikes, like so many other things in life, you can’t have your cake and eat it too.