The best definition for "super low" that I can come up with is "bitrates at which x264-encoded content becomes hilariously unwatchable."

I will try to be more specific. Youtube uses x264 to encode videos at a certain bitrate. Were you to encode the same video with libaom (AV1) at the same bitrate, the quality difference would probably be noticeable to a casual viewer. If you were to cut the bitrate in half and run the same comparison, the quality difference would be extremely noticeable to a casual viewer.