I'd say he was the best. I'm not talking about goal kicking, including field goals - anybody can look them up and make comparisons, but he could make the ball do wondrous things from hand.
I never saw him play at the ground but somewhere in the garage I have a commercial video of the 1980 Lions tour to South Africa with Afrikaans commentary that a rugby pal of mine sent me yonks ago. And I have the 1981 test games v NZ, before the curtain rightfully descended, archived on my computer. Old Naas was the most accurate, long kicker from either foot I have ever seen - and will ever see most likely, because the skill of kicking off both feet has gone a'glimmering, except with a few practitioners like Wilko.
Things disappear in rugby like the straight put into the scrum, kicking off both feet, and the 1950s ruck, (like a maul but with the ball on the ground.) They'll say it's progress and they are probably right, I suppose. Nobody had heard of a banana kick in the olden times.
I saw the great All Black fullback, Don Clarke play quite a lot in NZ during the time my parents moved there for about 8 years - both for the Blacks and the Mooloos. He was the longest kicker from hand I ever saw, but mostly from the right foot, and I doubt that Frans Steyn could ever place kick on old wet leather rugby ball like the great "Don" could.
I remember once looking forward to Don Clarke playing against Australia at Lancaster Park over 50 years ago and was disappointed when news came through that he was injured. I knew all about the All Blacks then, but very little about the Wallaby players having been in NZ over 5 years already, and in the time before TV. But it didn't take long to realise that the Australian fullback was doing everything that I had seen Clarke do.
Terry Curley was only 20 years old, and, as I found out later, played his first test for Oz at 18. The test match I saw was his 2nd last because he entered the priesthood when he got back to Oz. The Joeys lad could have been a Wallaby great if he had another calling.
The next best long Oz kicker I've seen was Roger Gould but the best tactical kickers were Paul Mclean and Noddy Lynagh. For the Kiwis Grant Fox was king but he kicked far too much because he was a poor runner. To some extent Mehrts was the same but he was more of an all round player than Foxy ever was.
Another tactical kicker I liked, if you can like such players, was Ollie Campbell of Ireland, but I saw so little of him that it doesn't signify except to say in hindsight that he was the precursor to ROG.
I'm trying to think back, with the keyboard in front of me knowing that somebody will mention the worthy Hugo Porta and others I have seen, but that will have to do for now having consumed my ritual two glasses of red with a late dinner.