How about the historical perspective?
Get in your time machine and go back a little over 20 years before GPS was even available to consumers. The only way to calibrate your speedo with pitot tubes or a paddle wheel was to time your boat through a known distance. A slalom course provided the known distance and there were well known tables to determine speed like this
http://sites.utoronto.ca/ski/water/faq/btspeedoadj.html I remember lots of dudes that knew those tables by heart and could quickly calibrate a speedo with just a stopwatch. Perfect Pass didn't exist. The best way to drive was to drive by engine speed (rpm/tach) with a mental calibration to the speedo (i.e. 3000 rpm = 30 mph) and men around the world yelled at their wives because they tried to control speed like a car and they couldn't get a smooth pull through the course. Perfect Pass was created in 1995 and it was dubbed "the marriage saver". IIRC, the first and only model was a tach based control which was basically like setting cruise control for 3000rpm. Wakeboarding is basically brand new.
Now fast-forward to about 15 years ago. GPS is available but not ubiquitous. Now you can calibrate your speedo without a course. Amazing! I remember borrowing a friend's Garmin GPS navigation device to do this and it was soooo wonderful since I didn't have access to a course. Check out this thread from 2005
https://www.mastercraft.com/teamtalk...ead.php?t=5077 They actually discuss the ethics of buying a GPS from Walmart, using it once to calibrate and then returning it. Wakeboarding is the defacto sport and drivers pick a speed based on wake shape and adjust accordingly. Consistent speed is more important than absolute speed like it was with slalom but there was still lots of room for preference: "I like to be pulled at 21mph". Perfect Pass is common but it's still a bit of a luxury option. I'm not sure when Perfect Pass released their Stargazer GPS option but it was right around this time and it was their flag-ship product and everybody rejoiced with the idea of an automagically calibrated speedo! Wakesurfing is basically brand new.
Fast-forward to about 5 years ago. GPS is now ubiquitous. We have a minimum of 3 GPS devices on our boat at any time. Calibrating a speedo to GPS is trivial. Perfect Pass or similar devices are basically standard (like A/C or power windows in a new car). Wakesurfing is now the defacto sport. Now people really don't care about the absolute speed, only wave shape. If I jumped on your boat, I wouldn't dream of requesting a speed, just "make the best wave". But at the same time, the speed control is even more critical. I can tolerate +/- 2 mph wakeboarding, but on our boat, the surf wave is more like +/- 0.5 mph and I can notice even even a few tenths. We could basically set cruise control by locking in the speed when the wave looks good without even calibrating the speedo but since I know ours is great at 10.5mph, it's nice to be referenced to an absolute speed.
Water sports have a speed and control problem going back to the beginning of water-skiing that has been elegantly solved by Perfect Pass and GPS in the last 15 years. So yeah, it's hard to let go of the idea that GPS is the best solution. Especially for the majority of us that are on lakes and don't have to consider currents or bridges. GPS works 100% of the time for us so there's no downside.