I agree with you, but I would like to point out that airplanes without power should glide, i.e. see gimli glider. I do wonder though if anyone has tried with recent Boeing models.
I knew most planes have quite reasonable glide distances and I knew that large commercial airliners were no exception. But from a relative standpoint (GA vs CA) this seemed suspect at first. Intuitively to me the enormous mass differences would make up for the wing surface area differences and the advantage would be to much smaller / lighter planes. On further reflection makes a lot of sense. Fuel is one of the highest costs of commercial airlines. Of course they are going to be hyper-optimizing for this where they can. A 747 being fuel efficient is far more important to bottom lines than a tiny Cessna being fuel efficient and with the relative costs of these aircraft, Boeing can invest far more in research to reduce drag and optimize lift. Aircraft glide ratios certainly seem to confirm this.
Airliner glide ratios fall between 15 and 20, which is comparable with cheapest immediately post-war training gliders for category B, aka the gliders you put a student pilot to learn how to make turns before the advent of two-seater trainer gliders.
And that 15 to 20 glide ratio is for best possible condition.
