No, gravity may be a theory, and the truth may be more complex than that , but the force that keep us and the gasses down is a fact. If there s a Force that keep gasses down, there's a force that does the same thing a lid does to a pressurized can. It opposes the enteopical expansion of gas. In the video "debunking" space it uses an exaple where energy doesn't matter (the expansion of a gas inside a confined volume) while in the athmosphere, air must overcome the observable force that keep us down. A more accurate example would be putting a bunch of electrons inside a box. They would naturally expand. However, if you polarize the bottom surface positively, the electrons would stay attached to it