Gears allow you to use a single motor in numerous applications because it lets you choose the prop best suited for the specific model, not to the motor. Just because a motor is running at 80% efficiency doesn't mean it will give the best performance. You can run at over 80% efficiency pretty easily with an x430 prop on a Titan, but that prop is too small to convert the power into forward motion.
The torque multiplication of gears lets you find the best sized prop for the hull first, then match it and the motor together. For oval racing this works pretty well, because the motor will be running in a rather small rpm window. For wide boat speed variations the gears will "compress" the usefull rpm window of the motor into a smaller speed window for the hull, but this is usually not a problem.
Dropping from a 1:1 ratio to a 1.2:1 ratio does not mean the amp draw will drop by 20%. It may drop by less, or by more depending on the hull and prop. I normally use gears by finding the prop the hull likes best, then changing the ratio to fit the motor to that prop and speed window.
[Gears also let you use a more powerful (lower number of turns) motor with the same cell count without overamping. If a direct drive 9XL drives an x442 well in your hull, putting in a 7XL with reduction gearing can let you run faster with the same prop at the same - or lower - amp draw.]
