That is correct. I am a Tennis instructor. I have 4 kegs that I use. CO2 is faster as the molecule is smaller. But the down side is that it also defuses out faster. I could not get plain air to inflate / infuse in any reasonable time.
I want to use kegs as pressure vessels to pressurize balls. I've tried to find the information myself but I cannot find it. Otherwise I would not bother brewers.