I thought I'd take a peek at the novelization of Star Trek: The Motion Picture
written by Gene Roddenberry himself. Folks may remember that as the movie opens, the V'Ger cloud attacks a bunch of Klingon ships. In the novelization, Kirk is actually able to "see" this happening. (An emergency signal was transmitted directly to an implant in Kirk's brain--a sort of emergency communication device.)
"Kirk found himself seeing three Klingon cruisers which appeared to be moving at warp velocity and in battle formation. The images became more detailed, increasingly real--he could begin thinking about them consciously. The Klingon vessels were big, dangerous looking--undoubtedly their new K't'inga-class heavy cruisers which some Admiralty tacticians feared might prove faster and more powerful than Starfleet's First Line Constitution-Class starships."
Whatever Gene Roddenberry's original intent might have been, it looks like that by 1979, he intended the top-of-the-line starships to be Constitution