From Inside Star Trek: The Real Story, pgs 391-3
BOB: ...But before any Story Editor was hired, Gene had a surprise for me. "Good news, Bob", Gene said, smiling. "I'm going to keep my Executive Producer after all. Star Trek's going to have a new producer this year."
"Great, Gene." This was what I had waited for. I would finally get the title to go along with what I actually did. And there'd be monetary recognition as well.
'Fred Freiberger's coming in as our new producer next Monday. He'll be a big help to me riding herd on stories and scripts."
I'm sure the smile froze on my face. "Gene, I thought I was going to produce. That was the understanding."
'Oh, you will, Bob. Fred'll be Producer, and you'll be Co-Producer."
It was like a good news-bad news joke. Only this one was on me.
It took a while, but later, the reality dawned on me that neither NBC nor the new Paramount TV management team would have agreed to my becoming the show's sole Producer. To them, I was a "nuts and bolts" kind of guy, not someone with enough creativity to run a complicated series like Star Trek. But if Herb Solow had still been at the studio, things would have turned out differently."
HERB: Fred Freiberger was an experienced television writer-producer who also had the good fortune to be represented by Roddenberry's agent, Alden Schwimmer...(skipping ahead)...Gene was then confronted with a choice. He could step up and fight for the equally shared credit for Bob Justman, or he could take the path of least resistance and not fight for his friend and associate. Gene took the path of least resistance. Fred was named Producer. Bob, who for two years had in actuality been the line producer handling every aspect of the show, was treated like an also-ran.
Gene was a stand-up guy for himself, but not, unfortunately, for others. Paramount Television and NBC preferred that a writer follow in the steps of Roddenberry, Coon and Lucas as the producer of Star Trek.
Television historically separated the producer function into creative and production, or "above the line" and "below the line", even though the two tended to overlap. In most instances, especially on difficult production series, the producership was equally divided. If the responsibilities had been divided on Star Trek, the Producer credits should have listed both Fred Freiberger and Bob Justman.