Whoops, sorry for finding the wrong post @Falco. Looks like you did remember correctly @codinghorror, apologies!
In my mind the correct value is whatever one respects the OS setting. If I have rotation lock on, the app shouldn’t be rotating. If I have auto-rotate on, the app should rotate like the OS does. Given that Android 9 supports locking the device in landscape, this will (hopefully) make everyone happy.
Side note, the Discourse Hub app functions as I just described above - it respects the OS.