Except it doesn't work, because every previous Trek series used "Terran" to refer to Earth people from the Prime universe, as science fiction has always done since long before Trek existed. (E.g. "Yesteryear" where the children asked young Spock, "Are you Terran or Vulcan?") So it's contradictory that DSC shows characters hearing the word "Terran" and immediately understanding it to mean Mirror human without any additional context. The problem is not that "Terran" is used for Mirror humans -- the problem is the implicit assumption that it is not used for Prime humans, which is incredibly wrong.