As many people mentioned it's not just HP but torque as well. Plus you have to consider where in the RPM curve these values are maximized. Most new vehicles with smaller engines making greater power do so at a higher rpm, > 5,000. This is not conducive to skiing where you need almost maximum torque at lower rpm's to get the skier out of the water and you also need solid HP and torque around 3,500 rpm for slalom skiing and jumping. That's why the 6.0 liter small block is ideal for this application. This motor paired with Zero Off is the perfect combination to give a great pull.
Unfortunately there is not a more efficient way to produce that kind of power. As many people said turbo engines will be hard to predict and control with the lag, gas or diesel. They already offer a supercharged engine that is big $$, lots of power but not necessarily more efficient.
I wish Nautique would finish designing their Electric 200.