This didn't seem right to me as intuitively thinner air would require much more power to move the same volume to propel you forward. My intuition fell apart based on the altitude which aircraft typically fly. Below typical cruise altitudes, the air resistance seems to overcome the additional thrust produced by the engines leading to lower fuel economy. It's not until you get above typical cruise altitudes that the are gets too thin to be effectively pushed by jet engines. In retrospect it makes sense because of course airlines are going to try to operate at the altitude which costs them the least amount of fuel. Go much higher or lower than those cruise altitudes and your fuel efficiency drops pretty quickly.
This does not sound coherent. Airliners consume more fuel lower down than higher up. And they definietly don’t “glide” them in the aviation sense.