All that exists of that challenge match is the 4th set, 10 games. All that I've seen, anyway. I did stats for it and they don't match up with Vines recollection. Granted, it's only one set. Perhaps the others played out the way Vines described.
Connors had 11 free points to Newcombe's 7. Connors served and volleyed 10 times in the 4th set, and he was winning his service games EASILY. Newcombe never got past 30. When Connors does stay back there isn't much of a rally. As pretty much happened the times he stays back at the Australian, it winds up Newcombe chipping to Connors forehand and Connors approaching after a couple shots. One thing. at the Australian, he lobbed Connors a lot. Not so much in Las Vegas. Again, though, it was only a set and Connors was winning his service games, the only time he would be at net, so easily. There weren't that many points for there to be a lot of lobs.
This was Segura's Connors. Knowing that, based on how he played in the other 74-75 Connors matches I have, I tend to think Connors mixed it up the entire match. That he was never consistently serving and staying back which is how I read Vines' take on the match.
Segura, in his book with Gladys Heldman, expresses some similar sentiments about serving and volleying on both serves simply because that was the way it was supposed to be done. Segura was talking more about taller players with less agility. The Stan Smiths and Clark Graebners. That they would be better off not consistently serving and volleying on second serves against elite returners. Better to work their way in on subsequent shots.
At the end of that book Segura breaks down, in depth, 4 of Connors' main matches in 1975. The 2 challenge matches and The US and Wimbledon finals.
My recollection was that he thought Connors served as well as he ever had in the Newcombe match. Just using the 4th set, I wouldn't argue. And he served big. Relatively speaking, I mean. Not big by Roscoe Tanner standards. Big, I think, by later Jimmy Connors standards.