Basically Apple is simplifying the whole process. You're trying to think about it too much. Photos have gone from working like POP email to working like IMAP or Exchange. A much simplified and better solution. When you delete the photo, it's gone everywhere just like how IMAP works. There is no such thing as delete from a camera roll. You either keep the photo or delete it. Deleting it means ALL versions are deleted. You no longer have to manage whether the photo is local on your device, in the cloud, or what particular device it is or is not still on. Like IMAP email.
Edits to a photo show up everywhere and when you decide to edit, you always work on the full resolution photo. And when you want to share the photo, you'll always share the highest quality version. When the Photos app for Mac is available, I assume Apple will allow you to upload photos from your Mac to start working with that app as well in the same IMAP-like manner.