You can learn a lot when writing V2 of a thing though. You've got lots of real world experience about what worked and what didn't work with the previous design, so lots of opportunity for making data structures that suit the problem more closely and so forth.

But did they write the backend from scratch or was it based on a number of “com.apple.libs.backend-core…” that tend to bring in repeating logic and facilities they have in all their servers? Or was it a PoC they promoted to MVP and now they’re taking time to rewrite “properly” with support for whatever features are coming next?