DS, I don't know how you can say:
...try teling to that to the pair of F15's who crashed into terra firma whilst confused about their altitude operating QNH/RPS under a RIS
If they had been on Ben MCDui QNH (bearing in mind there isn't normally a met stn there) or the RPS (which would have provided
enhanced terrain clearance) the outcome would have been the same. They hit the hill because they were flying at least 2000ft below SA (one presumes under IMC at the point of impact), regardless of QNH/RPS.
That said, I agree with the thrust of your argument.