How to edit photos with Photoshop Essentials from Photos.

You can use any 3rd party image editor of your choice with Photos. All you need to do is purchase the 99¢ External Editors For Photos from the App Store. This user tip shows how: External Editors in Photos Are Here

I recommend you upgrade to High Sierra and Photos 3.0. There have even many improvements and fixes to both the system and Photos with that upgrade.

I am disappointed that Apple has repeatedly deleted functionality of apps and system software to make things look simpler (I suppose)

Actually, it is more convenient with the Photo Editing extensions. In iPhoto we could only select one external editor. When I needed to switch between external editors, I had to go to the preferences panel and select it to a different editor. That was clumsy. The photo editing extensions are all listed in a menu and I can switch freely between them. And call selected services offered by the applications as extensions. I am doing many edits in Affinity. And Affinity offers several extensions. I do not need to launch the full application, just the extension with the tools I want - for example, Affinity Retouche or Afffinity Haze Removal. All are there at once to pick from. And there is even an Affinity photo extensions calling the complete editor. It is one of the reasons why I now prefer Photos to iPhoto (as long as I do not have to make a photo book).

In High Sierra we are able to call external editors directly from the "Image > Edit with" menu. But it is only working for a few applications like Pixelmator, that have already been updated to work with Photos. For most other applications I still need the External Editors extension, because they are not able to send the edited photo back to Photos.

. I have been reading some cautionary tales related to APFS and will probably delay upgrading for awhile.

It will depend on your Mac model, if you need to convert to APFS or not when upgrading to High Sierra.

See: https://support.apple.com/en-us/HT208018

The upgrade will only install APFS, if the internal drive of the Mac is a SSD.

When you install macOS High Sierra on the Mac volume of a solid-state drive (SSD) or other all-flash storage device, that volume is automatically converted to APFS. Fusion Drives, traditional hard disk drives (HDDs), and non-Mac volumes aren't converted. You can't opt out of the transition to APFS.

Consider to invest into the "External Editors" Photo editing extension. You can purchase it for 99cents from the AppStore. You call "external Editors" from the Edit page in Photos, and then select one of the editors you have installed. It makes it very easy to switch between external editors without having to change the preferences.

Which version do you have? I still have Photoshop Elements Editor 12 - it launches on High Sierra, but I cannot launch it using the "Image > Edit with ..." menu in Photos. But I can use it from the "External Editors" extension in Photos.

Remember you'll need to install the legacy JAVA from Apple before it will launch. You can get it here: Download Java for OS X 2015-001

Photoshop Elements V10 works with HS, both alone and thru Photos.

To launch Photoshop Elements.