Well, I just gave a try to Adobe Lightroom on my Samsung M52 phone
(Antutu score 520000). I used 20MP RAW files.
Seems that the processing speed is more than sufficient. When I moved
the sliders of the various settings, the changes in the preview were
instantaneous (I guess the small size of the preview might have played a
role). Saving the image to JPEG after editing took a few seconds.
Then I tried Lightroom on the tablet of my daughter (Lenovo Tab P11 Pro,
Antutu score 607000). Also there the changes were practically instant.
So apparently a phone or tablet with 500K Antutu is fast enough for this
kind of image processing.
An iPad 12 pro (> 1100 Euro here in Germany) is not needed. A Lenovo Tab
P12 for instance (Antutu 520000, 384 Euro) or a Samsung Tab S8 (Antutu
1039906, 639 Euro) might be sufficient.
A question is how to calibrate the screen. Not sure I can use my X-rite
The other thing is that PTGUI (pano stitching) doesn't seem to exist as
an Android app.