As anybody who has gotten past the opening chapters of The Emerald City of Oz knows, while Baum (whether deliberately or by oversight) left the question of whether Oz was an in-universe reality or an in-universe dream (even though Dorothy is completely absent from The Land of Oz, it could be taken as a dream in which she was a passive observer, invisible to the characters), from the opening chapters of Emerald City on, he came down decisively on the side of "in-universe reality." (For those who haven't read it, Emerald City begins with Aunt Em and Uncle Henry losing the farm to creditors, and Dorothy conferring with Ozma about moving the entire family to Oz permanently, something Ozma had wanted to do for some time; the rest of the story is, in large part, a fish-out-of-water story of hardscrabble farmers Aunt Em and Uncle Henry, who'd never known anything but scarcity, learning to cope with an environment in which scarcity is all-but-unheard-of.)
The liberties taken by Langley, Ryerson, and Woolf go beyond poetic license; by making their version unambiguously a dream-fantasy, they dropped the stakes to zero. If it had languished in obscurity, it would not be a sore point with me, but instead, it eclipsed the popularity of the books, and embedded itself so firmly in popular culture that in Return to Oz, Murch and Dennis probably felt obligated to include nods to it, nods that at best were pointless (e.g., the Nome King having the "ruby slippers" that Dorothy had obtained from the Wicked Witch of the East, instead of his canonical "magic belt"), and at worst, actively detracted from the story (e.g., the whole Kansas subplot involving electroconvulsive therapy to treat Dorothy's "delusions" of Oz).
In effect, the 1939 movie became a tail wagging the proverbial dog.
