Be careful with Shirer. He was a journalist, not an objective one. Nor was he a historian.
His work was, if you ask me, an early case of „advocacy journalism“, which, as another wise Freeper wrote, used to be called „propaganda“.
The fact that he was a fanatic Germanophobe, alongside the other assorted honorable (?) members of the „Society for the prevention of WW III“, doesn‘t help either.
He was what might be called a „Sunday-afternoon writer“ - and about Germany he and his despicable fellow writers, Rex Stout, H.T. Tetens, Eleanor Roosevelt and others of similar ilk, are about as reliable as Howard Zinn and N. Chomsky are on American history.
Yes, you can always tell an ideologue, but you can never tell him much, as the old saying goes.
The 1989 movie series “The Nightmare Years” was a jumped up version of elements of the Berlin Diary (which does read pretty well and the projections/prognostications pretty on point. He pretty well defined the Commie vs. National Socialist “spectrum” and finagled a lot of info right out from under Goebbels and the OKW.)- the movie tried to convey he was a “cutout” info agent for US Naval Intelligence in Geneva. None of that is in the “Berlin Diary”. Shirer had a falling out with his friend Edward R. Murrow after the war, and think that Murrow was not all he seemed- for sure. Especially as regards Paley at CBS.
Just as Hemingway knew all about Philby (Orwell wrote about this) when in theatre in the Spanish Civil War— Philby being a Stalinist agent long before he became DC MI-6 head...full time Commie spy. As far as is known Hemingway never let the Brits or our OSS know Philby was burrowed in. The intrigue of Franco’s lacky covered in “the Diary”, makes clear that Franco did not “bond” with hitler, and the Nazis could not drag Spain into the Axis no matter how hard they tried. Franco did not like Socialists or Communists. Interesting stuff.