You're right. GPX is really nothing more than a glorified .CSV file, kind of like EPUB is really nothing more than a ZIP file.

I would link to my spreadsheet but it looks like Apple Maps has changed slightly and it my spreadsheet method doesn't work as well as it did. I'll do some research and see if I can get it working correctly. I suspect Apple Maps has been changed in macOS/iOS 27.

I do recommend Guru Maps and I'm really liking Unpaved for NZ roads. Both have the advantage of using OpenStreetMaps so their data is reasonably up to date, unlike Google Maps.