Can't find all features of iCloud Photo Sharing with non-Apple devices It appears that the full complement of features of sharing a photo album with iCloud photo sharing is only open to fellow Apple devices.

For example, only Apple devices can subscribe to the album and then comment, like and add photos/videos (depending on my permission selection). However, If I want to share the album with non Apple devices, then I have to send them a link and they can click on the link and see the photos and videos but they do not have the option of adding photos or videos or liking or commenting.

Is this correct?
This is correct. Apple did not reimplement all features of the iCloud protocol in its Web interface. You can install Google photos on your Mac or iOs devices, if you like, but it has also its problems.