When you watch the video of him playing you do not see him adjusting his tone control like he does his volume control. He stated the tone control was either on or off. He stated he used that no treble side with his distortion as another color on his palette. He stated that the treble was recreated with the distortion. When he did not use that side, he used the other side. ON or OFF, pretty much exactly like what he himself stated. can it have a better knee, or altered to work better? it sure can, but that is not how he used it.
"The process of selecting the tone on the guitar is an aesthetic process like any other, so you try a lot of different things. Most of the things I’ve tried I’ve tried in live performances" ~ Jerry Garcia