If that were the case, it would not have been CANCELLED during its second season, only to be brought back due to the first mail-in campaign. And the lousy ratings stayed lousy through the third year.
Actually, most of that was Gene's bullshit, frankly. Trek's ratings were not stellar or great, but they were decent enough. Trek, behind the scenes, though, was a extremely troublesome show which the executives were trying to kill starting at about the second batch of first season - due to many, many problems with the cast and crew - many of which were pinned squarely on Gene. (Like screwing all the women on the set and then giving them casting bonuses that were against the law, and so on).
Third season only came about because Gene wasn't in it, but by that point, Desilu and NBC really had made up their mind. They put the show in the 'death slot' and slashed its budget. While some of the stars went on to do other things (Shatner, in particular), Trek became poison due to the reputation that the cast and crew had earned. Gene, himself, would take twenty years before his career would go anywhere again...