For many years Welles fans blamed Robert Wise for for cutting out scenes from the film for the theatrical release. Welles contributed to this, by blaming and resenting Wise for his changes and for Wise insisting that the released version was better than the original (which Welles naturally disagreed with). The truth is that before the first preview, it was Welles himself who asked Robert Wise to cut out a major scene from the film (George preventing Eugene from seeing his mother). This was a pivotal dramatic moment and it was entirely Welles' decision to remove it, a fact which only became clear once film historian Robert Carringer accessed the cutting continuity which has survived. Carringer argues that removing this scene for the first preview at Pomona played a part in the negative reception, and he notes that for the second preview, Wise reinserted (without Welles' consent) the same scenes back into the movie, and the Pasadena Preview played far better, but by then, the new management at RKO felt that Welles was Persona Non Grata and wanted nothing to do with, and they ordered Wise and another director to do reshoots and change the ending.
As for those blaming Welles for being megalomaniacal, it was he himself who surrendered his Auteur License despite still being on contract. He did this is an act of good faith to RKO chief George Schaeffer who was facing internal pressure for greenlighting Kane and backing Welles. It was Welles' hope that The Magnificent Ambersons be an uncontroversial subject, lacking in the topical and political criticisms in Kane so that it wouldn't bring controversy, at least not in terms of content. During the production of Kane, the US Government asked Welles to shoot a documentary in Brazil as part of the Good Neighbour Policy which kept Welles away from America for most of the post-production, and as a result of poor communication during wartime and the difficulty of getting a via, Welles was not able to properly communicate with Wise, nor was Wise able to travel to Brazil to edit the film as both he and Welles originally intended.
In retrospect, historians argue that with Ambersons, Welles simply failed to understand normal studio politics. On Kane, Welles was given the red carpet with the likes of Gregg Toland, producers George Schaeffer and John Houseman as well as well-wishers like John Ford and William Wyler protecting him from dealing with the pressures of RKO's management and publicity department and simply focus on making the film, more or less working similar to how he worked on his radio and theatrical productions. For Magnificent Ambersons he was on his own, and RKO chiefs who were skeptical of Kane's negative reception and controversy with Hearst, were willing to make use of the smallest slips and mistakes to rid themselves off his contract.
Narm: One of reasons for RKO's Executive Meddling. Preview audiences laughed at several scenes that were intended to be extremely dramatic.
Values Resonance: By the dawn of the 21st Century, with the decline of American auto, and the rising consensus against car cities, Eugene and George's debate on the efficacy of automobiles gains renewed currency.