> Most internet apps are read-heavy, there are more reads than writes, so largely it makes sense to deal with the latency on writes. We can do this by forwarding the writes to some leader for that piece of data (e.g. the log for usernames), and waiting until that write is replicated back to us (so we can read our own writes).

This is precisely the point. For most CRUD applications, writes are usually so sporadic and user-intentioned that you can show a spinning wheel for it, and users will forgive you for that slowness because it's so sporadic.

Edge computing is basically reinventing insecure HTTP caches and mirrors, but allowing you to include authn/authz so that user data stays private to them. If your edge data model is that much more complicated than that, you're probably doing it wrong.