Paul,
The fallacy in your example is simple. When the current scoring system was created, a 120 second low speed time (15 mph) was a real achievement. Most folks were thrilled to achieve 90 seconds (20 mph). Without sliders, a 90 second low speed was generally not a "rock up to 20 degrees AOA and putter the circle" type of flight like a full size aircraft in minimum controllable slow flight. It was often a saw tooth flight path with periods of dead idle and periods of near full power (for a ST C-35, for Profile).
There is a second fallacy in your scoring example. 80 mph was not a common profile high speed for that time. That level of speed didn't become reasonable until the modified OS 40 to 36 conversion and K&B 5.8 engines became available and didn't become common until ball bearing engines were allowed (1978 or 1980?). 70 mph was not a common Class 1 or Class 2 speed in that time period. So it would have been very unlikely that the performance example you used is a valid example of how the scoring system treated two competitors. Those flight performances would not likely have been in the same class. The differences in performance would have been much narrower within a class or the competitor wouldn't have been competitive on that day.
The current scoring system was created to balance the scoring. The current flying performance levels are what have broken the balance.
Look, people quit an activity for a number of reasons. I've watched folks drop an event not because of a rules change, but because someone 1500 miles away has a new killer engine. It doesn't matter that the new engine is unreliable. It doesn't matter that they will never, ever, actually see or hold the engine in their hand much less compete against that engine in the event. The mere existence of the engine and that had been used in the event somewhere was sufficient for them to throw in the towel.
We had lots more folks participating in the hobby when they had the time to participate. When the expense and effort required didn't hurt. We had a lot more participation when we went flying with our friends. We had a lot more participants when it was fun to go fly. The rules revisions didn't change any of those fundamentals.
You want to build pretty, build pretty and enjoy flying it. You want a McCoy 60 Sterling Guardian, build it and enjoy flying it (I'll take mine with an OPS 60, please). Don't like sliders? Don't use them. Don't like prop hanging? Don't do it. Want 10% fuel? Use it. Want 79% fuel? Tip the nitro can!
I have my Nats trophies in Carrier from the 70's and 80's. My son and I have his, mine, and our Nats trophies in Racing and Speed from the 90's and 2000's. Can you tell me which ones he/we/I won? I can't. So what is their value? They trigger memories of good times together with each other and friends in a setting we enjoy.
BTW, we compete in F2C and have done so internationally. The AMA rules are sane compared to some of the things you find in the FAI rules. And the event is fun for us.
The scoring system change didn't kill Navy Carrier, line sliders didn't kill Navy Carrier, and the prop hanging slow flight didn't kill Navy Carrier. What dropped Navy Carrier to its current participation level is people dropping out rather than accepting the challenge of the new environment or changing the environment to something more acceptable to them. What dropped Navy Carrier to its current participation level is not having new folks coming into the event. Folks like Gerry Deneau and Rusty Brown mentored me when I was new to Navy Carrier. The folks I've mentored dropped out long ago. But all of those folks dropped out for life reasons and may come back some day. They didn't drop out over some petty disagreement over the rules.
Don't like the current event? Run your own contest with your own rules. If it is successful, I'll be glad to offer my congratulations. If it isn't successful, you at least did something beside complain.
Dave