Of course, it's ironic that you list Johnny Cash - brings us right back to Sam Phillips. Listening to Cash talk about Phillips on radio's Fresh Air, it was clear just how much Cash really was *produced* by Phillips. Maybe he would have become a star anyway without the start he got at Sun, but maybe not.
Not to pick too many nits, but of the S&G LP's listed, as far as I can tell only P,S,R,&T listed Johnston as producer(this based on quick web research - my LP copies are in my storage unit as I write - also ironically, Wednesday 3AM, S&G's less-successful all-acoustic first LP, was produced by Tom Wilson). The popular Byrds stuff was produced for the most part by Terry Melcher, Gary Usher, or Jim Dickson. Of course, none of that means he wasn't involved on one level or another with everything or everybody you've listed - I'll go read the interview, thanks for the link.
However, I would not agree that any of above-mentioned producers have anywhere near the overall importance of Sam Phillips. Phillips was a visionary who not only basically created the characteristic slap-echo sound of rockabilly, he recorded Jackie Brenston's (really Ike Turner's) seminal #1 R&B hit "Rocket 88", often cited as the arbitrary 'first' rock & roll record, which launched Chess Records into the big time independents. He can only be discussed in the same league as such producer/engineer/label owner pioneers like the Chess brothers or the Ertegun brothers. In his operation, he was like a rock & roll Alfred Lion and Rudy Van Gelder rolled into one. If he had done nothing beyond just recording Howlin' Wolf's first sessions, his place would still be secure, but he also recorded Rosco Gordon, Rufus Thomas, BB King, Walter Horton, Bobby Bland, Little Milton, Honeyboy Edwards, Junior Parker, James Cotton, Sleepy John Estes, Ma Rainey, Earl Hooker, Johnny Ace, Pinetop Perkins, and many other lesser-known blues and R&B lights, many of who's Phillips sides were released on other independent labels before he created Sun and discovered Elvis, et. al.