I kinda agree with your conclusion, but feel that you are inventing a lot of unlikely and unnecessary maybes in order to get to that conclusion.
Yep. If I was doing any more hand-waving here I'd be gaining altitude. I have no academic/professional background in any of this to give a foundation to those hypotheticals that I'm throwing around.
Diving is not, for most people, a high-risk activity. It does not even have high physical requirements for most people.
I submit that diving is, for everyone, a very high-risk activity, just from physics and the fact that we can't breathe underwater without help. The equipment and industry practices and very easy dives for most warm-water-pretty-fishes divers combine to
manage the risk very successfully, resulting in a low rate of incidents. People who choose to dive (after the DSD) should be well aware that it's risky -- the types of serious events that can happen are emphasized in OW training.
For a contrast, take skiing -- a very cursory literature review (thanks, google!) suggests a much higher injury rate than for diving...something like 2~5 injuries per 1000 skier-days vs SCUBA (~0.3 injuries per 1000 diver-days), but a much lower fatality rate (80~100 skier deaths annually out of ~400M skier-visits/year) compared to SCUBA (150~175 deaths annually, from about 30M dives/year, or about 15~20x the risk of fatality).
Does this mean that skiing is
riskier than diving? Sure, if you're measuring the absolute chance of any reported injury. Does this mean that diving is a
higher risk activity? Sure, if you're considering fatalities (and, without any numbers, I'd say that a serious non-fatal DCS/barotrauma incident has a larger affect on long-term quality of life than an ACL tear or collarbone fracture -- the most common serious skiing accidents).
For me, and most people, risk isn't an absolute...it's some kind of combination of "likelihood" and "severity".
I agree that diving doesn't have high physical requirements. That doesn't mean that it isn't physically taxing -- even a relaxing drift dive leaves many people chilled and tired, and the dive professional is doing a lot more work than the customers before they arrive, during the day, and after they leave.