That Was my point that you can’t do a Time Machine back up of the photos. You also can’t download From the cloud and keep on the external drive. You would have to manually in blocks download and save to files which would take ages.You can plug any USB storage device into an iPad just as you can a Mac. It’ll show up in the “Files” app exactly as you’d expect it.
You can’t do Time Machine backups, granted, but that’s not the only backup option.
Besides … almost everybody has photos stored in iCloud, which, while not a true backup, is a thousand times a better backup than what almost everybody did before iCloud.
(Note: “almost.” Those who made real backups, such as to tape that got sent offsite, are a practically non-existent minority. Even those who just made copies on Zip drives to stash in a closet … within rounding, didn’t exist.)
b&
you also can’t import music into an iPad and move it to the music app.
For those reasons it should be used as a secondary device unless you aren’t bothered about backing up your photos.