So replacing a sky would qualify as "pure photography" (a BS term as I have ever seen).
By the Ansel Adams definition, as outlined here, yes. As would an AI-generated photo, since it would be precisely made to imitate the technique and content of a typical "photo". Uelsmann's photos would be pure photography, also, since they are combinations of photos.
Lots of things were more difficult then and the composites that are a snap of the fingers now were beyond the imagination of Adams writing something like that.
It makes more sense now to reserve the term "straight" photography to mean non-manipulated in destructive or intrusive ways. So whatever the camera provides to whatever least intrusive production of it (scan, print, enlargement - with minimal enhancements (dodging, burning, contrast adjustment, dust spotting, sharpening) that do not disguise or otherwise distort the content).
At this point in time, photography includes many techniques that are not derivative of other art forms yet completely change the content of the photo. And, furthermore, it is absurd to try to preclude from photography considerations that were not first grounded in other forms of visual art. The entire idea of composition, for example, predates even the faintest glimmer of anything photographic.