I started using spar varnish about 30 years ago, after getting to know many of the top professional stockmakers in the business and finding they used it almost universally. They were also kind enough to explain why, and the reasons are the same you just listed, with a couple of other minor details.
Chic worthing used Tru Oil last I knew as did Jack Belk. Dennis Olsen of Plains MT used Varathane for years. All are better than just good at stock work.
