As everyone knows electric motor input power in watts equals volts times amps. The similar relationship in piston engines is power equals cylinder pressure times displacement times rpm. Regulating the displacement in IC engines forced innovations that resulted in smaller engines with higher cylinder pressures operating at higher rpm to generate the same power. Think the 1956 Chrysler 300 versus today's Honda Civic type R both with around 300 hp. This pace was slow in both model and full size engines. However a 1950s model engine like the McCoy 60 produced around 1 hp while today's similar size, tuned pipe engines can produce over 4 hp.
Today something is happening much more quickly in electric power. Think golf carts versus the Tesla model S. Lithium polymer batteries were a game changer. Their very low internal resistance allows much higher currents than previous battery types. Before this batteries were the limiting factor. By only regulating input voltage with lithium polymer batteries we encourage innovation in motors and speed controls. This innovation today allows close to 30 hp input power (600 amps times 37 volts) for short times like SAW runs. With 1200 mah packs 400 amps will still give a 1.8 minute run time, enough for a standard heat race. Commercially available speed controls can deliver over 300 amps when water cooled.
One solution has been the P limited classes. By restricting the motor, it becomes the "fuse" limiting power. If you restrict the ESC choice, that limits power as well with the ESC as the "fuse". How expensive do you want this current limiting method to be? Motors are getting inexpensive. The fastest P limited racer in our club paid $27 for his motor. Competition airplanes use a more elegant solution involving electronic controls that limit input power. Simpler solutions that have been race tested involve limiting propeller diameter as well as motor KV and size.
Another solution has been to limit hull length. I watched Brian Buaas set two lap records in several voltage classes with the same small sport hydro. It just got harder to drive at the higher power levels. T class boats can be 60" long, the NAMBA maximum. The most powerful IC engines in a twin configuration probably deliver around 10 to 15 hp. Do we really want to allow electric power plants with more than twice that? What are some other current limiting rule proposals?
PS: Engineering is done with numbers. Analysis without numbers is only an opinion.