Yes, Adams and Mortensen were not exactly appreciative of each other's work, that is true, but really, it had nothing much to do with the zone system. The ZS became a religion only later, and Adams was not part of the congregation. Maybe we owe that to Minor, at least in part.
The active polemic was actually between Mortensen and Weston in the pages of Camera Craft, which was published in San Francisco in the 30's. The text of the articles is extremely interesting because it expresses the turn of conventional vision away from the kind of idealization of classical cliché themes that we see in movies of the period (Mortensen sold lighting equipment of his own design, consulted in Hollywood ,and knew most of the movie personalities, many of whom were his models). His work is really a part of the Hollywood kind of vision, from that particular era. He was a consummate master of lighting technique and also in the application of light to produce desired effects on the psychology of the viewer.
Weston's argument represented the emerging modernist vision. You will see his attitudes stated explicitly in the Daybooks. If you haven't read them, it is a good read. The photograph should do what the camera does best; represent the subject objectively, faithfully. Likewise, for comparison, the modernist would demand that painting do what painting is; that is, the subject of painting is paint. The camera needs to be used as what it is, not to be confused with a brush.
In the view of Mortensen, the picture was the thing, whatever it took, and he would do it; his images are as much or more paintings than they are photographs. It is interesting to look at some of his examples that show the before and the after examples, where he shows the photograph and then what resulted from his manipulations. He'd add castles. He worked from drawings, then set up the photo session to give him the image to manipulate. The photograph was where he started. It is also instructive to study his work in relation to HP Robinson and Rejlander; they worked in similar ways. Robinson drew and collaged his ideas, working up to the final version. Very similar, and similar, also, to practice current in advertising even today. Think of the concept, draw it up, and hand it to the photographer for realization.
The argument revolved around issues like pubic hair. Mortensen thought it was tasteless and obscene to include it in a nude; Weston thought it was obscene and tasteless to pretend that it isn't there. Weston showed it, Mortensen erased it. That pretty much sums it up. Differing morality, differing views of the purpose of art.
When the dust settled, the f/64 vision became the dominant for some forty years or so. Mortensen faded into the background, still selling lighting stuff in Hollywood. However, we still have pictorialists, but they are no longer called pictorialists. Most prominent, of course, would be Jerry Uelsmann. And even among the f/64 people (it wasn't a real group, and had no dogma, just an alignment; Weston himself dropped out after the first meeting) there is a really blurry line. Minor White's work takes the representational aspect and sends it a packin', his pictures a sort of visual mysterium. Yet, we have a hard time wedging him into the pictorialist box, even though his roots were deep in the Portland (Oregon) Camera Club. I suppose the difference might be that he left the recognizable or created scenes that seemed imbued with something from another world, rather than the reflections or expressions of conventional mythology or social cliché.
When I was a student in the 60's, to be called a "pictorialist" would be a challenge to fight. We were supposed to be true believers. Pictorialism, however, is no monolith. There is not just one "pictorialism" but many. A lot of it has been pretty darn exciting. I'd definitely recommend to anyone a look at Mortensen. If you ever get a chance, check out his _Monsters and Madonnas_. Also, if you find it, some of the work that was done in the camera clubs prior to WWII. The Seattle Camera Club, for example, had many Japanese members, many of whom were subsequently interned in the relocation camps. Much of the work that came out of that club was just simply incredible.
We are lucky that we don't have to believe in one or the other anymore. Or even to believe that we have only the single choice between the one and the other. Well, we never did have to, but in the 60's, most of us did.