AuthManager::changeAuthenticationData is not allowed to fail and returns nothing. Unexpected failure can be handled with an exception but unexpected partial failure (e.g. the data change was successful but a notification email should have been sent and that failed) can't, so it would be better to return a status object so that partial failure can be communicated to the user. Even when there was no failure, sometimes a provider might want to send information to the user, which could be done with a status warning.
That second use case also exists for the other flows which return an AuthenticationResponse. A status would probably make less sense there but the ability to return an array of messages would be nice.