From what I've gathered from Python and listening to his interviews....I think he sees a "designer" like a director would be on a movie. Someone that oversees almost every aspect on a game. I think the most accepted definition of the title "pinball designer" is the person that actually lays out the playfield and shots.
I think he personally took on the tasks of art and concept on most of the games he was involved in. I also know he worked closely with the mechanical engineers to design things on different machines he was involved with. My guess is that in some areas he was probably much more involved and hands on than other designers, but in other aspects he was more hands off and was just guiding the others on the design team in the direction he was wanting them to go with the game.
He also seemed to be quite a workhorse at Williams if you look at how close his releases were to one another. It seemed like one of his games would be released...then designer B...then another of his....then designer C...then another one of his...then back to designer B. It reminds me very much the way Borg was / is at Stern. If you need a game and are short on time....give it to the workhorse. They will do their best to get something put out in a hurry.
Python is incredibly talented, creative and passionate about pinball...and not afraid to show it.