"I don't think Gullett had that much to do with Schourek"
This is incorrect. Don spotted a flaw in Pete's delivery (something about how Schourek took the ball from the mitt and into the pitching motion, IIRC) and the change immediately improved Pete's command and velocity. Schourek was runner up for the Cy Young the year after joining the Reds, but before Gullett worked with him he was a soft-tossing journeyman lefthanded pitcher
I don't recall reading that Schourek ever threw 93 mph, prior to major arm surgery. He threw junk in the Met's bullpen because he didn't trust his fastball
Never overlook the obvious