That's a fine personal credo to have, and of course anybody with those beliefs should be able to give that opinion in respect to their personal work. Where I draw the like is in openly judging others, telling them they're doing something dishonest, calling their photographic works invalid, etc.
As with most things, there's a spectrum. In the area of wildlife photography, it would be ridiculous to accept an image with a completely or mostly manufactured creature (either drawn digitally or generated by AI), because part of the process of this art medium is 'capture'. In the other corner is the purist, who would hardly even dodge/burn in a darkroom., insists that it is only capture, nothing else, not even removing a distraction in the background. Then there's the rest of us in the middle.
Obviously, painting is hand created imagery in it's entirely. But it would very easy to impose similar rules there, require they accurately paint only what the eyes see (no adding or subtracting). Because that's exactly what the purists are doing in photography. And painting is not restricted to a single process: many fine works are mixed media, or in the case of printmaking, multiple-plates pressed into a single print (see Salvador Dali for those that need an example)—this compares well to composites in photographic post-processing.
Photography and painting are both canvas art, regardless of the canvas material.
And both have areas of representation of truth, such as photojournalism and courtroom sketch artist professional.
Chris