This is actually intended. The idea was to not change the behavior for existing instances, as admins might not be aware of this new feature and want to keep the current behavior (prevent users from disabling inherited rules).
The default value is true but it only applies to new instances.
Thank you for your suggestion.
Your feedback will contribute to some ongoing discussions about the release notes and the best way to communicate about new features and updates.
We generally reserve the Upgrade Notes for detailing the most important changes that administrators need to know before upgrading their instance. This piece of documentation is not typically where we document new capabilities.
For that specific case, it seems to me that the official announcement already provides quite some information on this topic.