Part of the problem might be that certain Adobe apps and their formats are pretty much industry standards.
The Affinity suite will output all major print and web file types and has robust colour management, the problem is with cross-compatibility of live files between Adobe and the Serif stuff. Although Publisher will open .idml files and Designer will open .ai files, neither can save back to a file that is editable in the originating Adobe app. (In
theory a PDF output from Designer should open as an editable file in Illustrator, but despite the PDF being 100% standards-compliant, Illustrator makes a mess of it. The dev team at Serif has looked at this issue more than once, and it's something that's happening at the Illustrator end of the workflow — even if it's not intentional, it doesn't seem very likely that Adobe will fix it, since it solely benefits people trying to migrate their workflow away from CC.)
If the OP could persuade their designer to do this job with the Affinity suite (it's not
that much of a wrench to move over — the PS/AI/ID equivalents operate in pretty similar manner) as long as the workflow remains within those applications, the end print files will be indistinguishable from the same job done with Adobe apps. In fact, for a brochure, you'd probably only need Publisher, since Publisher recognises .psd and .ai files (with the "PDF compatible" option used) as valid, placeable image formats. If we're only talking about tweaking layouts and making text changes at the client end, the designer can do all the usual design/artwork elements in AI/PS, assemble and typeset the document in Publisher rather and InDesign and send the resulting .afpub file to the client for amends. Not, perhaps, the most
elegant solution, but workable, I think.
[Edit: mentioned the wrong app in the final para.]
