One thing I hate about Musk saying things like "They have fewer accidents than people" is that it is only able to be engaged in the easiest of scenarios. So per mile, self driving on the easiest roads barely has less accidents than a human in adverse conditions? That doesn't seem to actually be better than people yet.
Yes, it's important to understand the limitations of the metrics, but the existence of limitations doesn't mean that the metrics should be thrown out entirely.