And yet photographers are able to use various Adobe (or similar) products to do real-time edits/sharing of their work. Most people don't need 100% control over the file-system. As long as the particular type of file they manipulate is available in the app they want to use, an iPad works pretty well.

If they have a single app/app suite that does everything, then sure that's fine (as long as it isn't things like copying a lot of data off an SD card or whatever) - the OS doesn't get involved much.

That isn't a common use case unless someone is paying a ton of money for a single, specialized piece of software that does everything they want, and the iPad only is used for that one thing. Which is a very limited subset of 'work'.

Many professionals beg otherwise, and are perfectly fine with documents as central concept of work unit, similar to Xerox Workstations.

That's not how the iPadOS treats files. Things are 'owned' by a single App, which makes moving data around or working on a common thing a real PITA except in very specific cases (and even then, it is often heavily controlled).

It's a 'App as a central work unit' type workflow, which is fine as long as you don't use more than a single piece of software/app to work on something.