I don’t know if Google Camera would share the information with Sandboxed Google Play. However, something to be careful of, is if you have two apps by the same developer (Google in this case), and you have network permissions for only one of them. The developer could share those permissions with their other app. TheHatedOne did a podcast episode on this. He checked with a GrapheneOS developer beforehand, and found, that this is possible.
I wonder how many users Matrix has?
I’ll give it another go with your suggestion
If what you proposed was put into practice, we wouldn’t have hundreds of distributions. I think the amount of distributions that exist may actually be overwhelming to a new user. If there were only a few distributions to choose from, you wouldn’t have so many people distro hopping, which is a waste of time (in most cases). You don’t like the desktop environment? Install something else. You don’t like floating windows? Use a tiling window manager.
Ultimately, it depends on if it is an issue in terms of your threat model. I have noproblems with people using some proprietary tools. Sometimes you do need things to just work, unfortunately.