This observation by Arnold Jacobs is why I find breathing exercises out of The Breathing Gym so beneficial for students. Getting them to experience the sensation of taking in a large amount of air without having the horn in their hands is invaluable and gives them something concrete to model when they do pick up the instrument.
Doing exercises with long inhales like 6-7-8-9-10 or any variation of In for 8 > Hold for 8 > Out for 8 (also 8>16>8, 12>12>12 or even 16>32>16) are great for feeling the sensation of moving a lot of air.
And as always, Mr. Jacobs was dead on with this observation. So often, mediocre brass players never get close to full and never get close to empty. Getting them to experience this is a great way to encourage them to eventually do it on their own.