BUT THEY USED TO IN IPHOTO! It was USEFUL. It WORKED. It worked WELL for YEARS.
I know, and i used it for troubleshooting the iPhoto library, when I suspected corrupted image files.
If Apple can allow this feature for FCPX and iTunes, then surely they can allow it for their image editing app.
The management of the Photos library is more complicated than it has been for the iPhoto Library. When you revealed the original master file in iPhoto, you could be sure, that this particular copy was the one that iPhoto has been using. Now we have the added complication that the original master files may be syncing with iCloud, and it will be hard to tell, when it will be safe to access the originals or edited versions, even if you quit Photos, before you try to read the original files.
After I migrated my photo library to Photos, I noticed, that some of the original image files had missing EXIF tag and I wanted to add them with exiftool. In iPhoto I could simply reveal the originals and tag them with exiftool right in the Masters folder.
In Photos it does not work to edit the EXIF or IPTC of originals, once they have been imported. It is easy to find the original files in Masters, if "Download original files to the Mac" is set, but modifications to these files do not take most of the time, because it is hard to tell, if and when the files will be read or overwritten by synced files from iCloud. I think, Apple discontinued the "Reveal in Finder" option, because the location of the original file is uncertain, if syncing with iCloud Photo Library is active. And if you do not enable "Download original files to the Mac", there may be no original files to reveal at all.