When two devices write to the same field, the update with the latest timestamp wins.

I'm confused. That update is not conflict free. It resolved the conflict by deciding one of the two wins, without resolving the underlying difference (add and subsctract must be combined/summed up).

Most systems ask developers to write manual conflict resolution code, but that’s error-prone and hard to maintain.

In my eyes, we resolved the difficulty by ignoring correctness.