David, I came up paddling in the 90’s, and was doing mid class 5 when I married and had kids, basically retiring from that high end of it. What I was taught then, (I knew and paddled with Charlie Walbridge) was anything much over 20’ or so you were taking risks outside of skill, that the possibility of back injury was just too high. I paddled some of the classic 20-25 footers in the NE US, but never took it beyond that.
The reason more people die in class 3 is there’s a helluva lot more people paddling it, and tend to be with lesser skills and experience. Class 3 rivers like the Lower Yough in PA and the American in CA get tens of thousands of paddlers a year. But that doesn’t mean the people taking undue risks in class 5 aren’t being irresponsible. By me, class 5 by definition means there are things out of your control. Wood, undercuts, just the turbulence and power can mean serious consequences. Compare it to Alpine climbing vs trad, there’s just so much more that can go wrong, that underplaying it serves no one.
There’s a documentary about paddlers by Kate Geis, Riversense, that among the featured were a paddler couple who were doing extreme class 5 after having a child. The man said he had such skills he was not taking risks. I thought this was delusional. I had the worst pin of my career on the Cal Salmon when my son was 15 months, and that was that. My sport was not worth not seeing my kid grow up. That kid is now an avid trad rock climber, and terrifies me!