Thanks for the replies!
For me, changing the Download features isn't nearly as important of a feature. In fact, I can live without it, as I've never really interacted with it anyway. I enjoy the larger view that happens when I click on a photo in an album, and I think most of my friends in my groups also use this to view individual photos.
I'm sorry that changing to a stable URL means a new data structure. Could that be done though? This would really improve my groups' ease of use by a tremendous amount. I think the fact that it has been suggested multiple times shows the need for it.
I know I'm speaking for hundreds of users when I ask/beg for it. It would be INVALUABLE for our experience. As it is, archiving messages that refer to photos is so much less effective since those photo links often end up pointing to the wrong thing. I know newer members to our group find it hard to get a lot out of archived conversations because of this. (We are a visual arts group).
I hppe this change can make its way to the "to implement" list for the folks that produce groups.io.!