Terence, I appreciate your expertise, but there are several use cases where your solution does not work. For example, I am using an older version of Adobe Photoshop and I can't access the files in Photos through the Open dialog in PS, I can't drag and drop from Photos to PS and I can't use Adobe Bridge to open from Photos. The "best" solution at this point is to copy from Photos into a folder on the Desktop and open from there, creating duplicate files. This adds two steps to my workflow... very un-Apple like.
The absence of drag and drop functionality between applications is a fundamental flaw in Photos and should be resolved ASAP. I've submitted product feedback already and encourage others who find this thread to do the same at https://www.apple.com/feedback/photos.html