Where I'm coming from is getting dumped out of a room that switched to spaces, and the room's server's admin telling me they got an error message that my homeserver does not support that room version, and my homeserver's admin saying they're on afatk the latest stable release of synapse, and then checking the spec and finding no mention of that room version at all. This is an absolutely trash user experience and certainly colored my response. As it is, I can't speak in said room and the room admin doesn't know how to fix that and neither do I.
The problematic room's server's admin must have been misinformed in this case, that's where I have the info about v9 being the default.