Oh, Adam. My apologies. I see that the successful files are .HEIC which Adobe is seeing as RAW and treating accordingly. That was sloppy testing on my part.
My thoughts though are that these days, with storage getting cheaper and cheaper, isn’t exporting a larger, uncompressed (Maximum quality) JPEG with metadata the least intrusive solution to getting a file with embedded metadata out of Photos? It is smaller than a .tiff and what it gives up in storage it saves the client the time and cost to duplicate that lost metadata. If it’s that important to get out of Photos?