Canonicity has nothing to do with authorial oversight. Ufotable has the rights to produce Demon Slayer content, and therefore any media they produce falls under Demon Slayer canon unless explicitly stated otherwise. Furthermore, authorial approval is sufficient to grant work produced under the story's rights to be canon, if it wasn't clear already. Legally speaking, the work is absolutely canon because it was created and approved of by the holders of the copyright. Unlike Kimetsu Academy, where there is absolutely reason to believe that it's non-canon (and it in fact isn't), the anime adaptation of the manga is fully canon, including the Mugen Train movie, and is material drawn directly from the manga (in some cases word for word, panel for panel).
There is no grounds to consider the work non-canon. The mangaka herself has stated in no uncertain terms that she considers the adaptation to be an amazing adaptation that everyone should consume, which alone should be enough for it to be canon since authorial approval of adaptations is literally the grounds for canonicity. That it contradicts your argument doesn't make it not a copyright holder approving of the accuracy of a work to their creative vision. That's the textbook definition of establishing canonicity.
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