SimP I agree with your premise but actually a lot of TMO appointments this season havs been existing referees but you are right, it is referee led. Barnes is one of the worlds best in explaining what he thought he saw and then using technology appropriately.
On 2 occasions TMO suggested a review and on both Barnes went with what he had seen in field, with no loss of standing to either party.
Similarly Peyper pleased me that he used technology to see how Jack Nowell had ended up being under the jumper. Whilst I wasnt convinced it was an England penalty what it did show was it was definitely not a YC or worse a RC.