I guess it depends where your priorities lie, but this effort seems _more_ sustainable to me because it can run most proprietary android apps, and everything on F-Droid right out of the box.
PureOS has to try and reimplement an entire mobile app ecosystem just to get to parity with existing competitors.
The way to go, IMO, is having Android emulation on your device for backwards compatibility.
SailfishOS has this, and doesn't do tracking.
PureOS and Purism One implement some FOSS techniques and rebrand them. I believe Nextcloud does this as well. Not sure why projects don't clearly mention what they're based upon, especially when its a lot like original.
The thing is, there aren't any desktop apps—much less Linux desktop apps—for the types of things I need to do on my phone. On an Android phone, I can buy train tickets (NJTransit), deposit checks (Chase), and have telemedecine appointments with my doctor (MyChart).
I don't know if all of these would work in e.foundation, but presumably at least some would run.
Unfortunately, I chose all of those examples explicitly because they can't be done on the web—they can't be done on a desktop device at all! :(
The telemedecine app is a big one I think about. I don't know what I would have done if I hadn't had a modern iOS or Android device when the pandemic hit in March, and my doctor appointments suddenly moved to this remote system.
PureOS has to try and reimplement an entire mobile app ecosystem just to get to parity with existing competitors.