I’d like it be possible for write/edit capability to be disabled/enabled in preferences. That said, I disagree about not allowing Photolab to edit data. The whole point of portable XMP data is for all the applications to touch the metadata without changing its structure.
Of course, the mess with hierarchical keywords which you and @Joanna are exploring in detail (very informative posts, thank you both) indicate no cross-compatibility between any of the major players. It makes me happy that I’ve avoided hierarchical keywords. When I saw Adobe push for them in Lightroom I knew ahead of time it was a death trap of the Microsoft “Embrace, Extend, Extinguish” kind.
Outside of hierarchical keywords, most tags should be shareable among major applications. Title/headline, description/caption, creator, location, event, etc. I’d enjoy the opportunity to be able to occasionally title and caption images in Photolab while doing most of the metadata batching in Photo Mechanic. Of course I’ll never get the chance as DxO offers next to no support for macOS (OS -1 is not support, it’s a kick in the face, DxO has fallen in my opinion into the category of non-professional hobbyist software with this policy).