Think about airplane engines. Lycoming and continental run low rpm large displacement pistons to make horsepower. Auto engine conversions uses a prsu (propeller reduction speed unit) to turn the propeller slower than engine rpm. Auto engines use high rpm lighter pistons to make horsepower. The lighter pistons wear less, time between overhauls on planes 1000 hours = 50k, 3000 =
150k. Would you be ok with overhauling your car at 50k miles?
Even most of the ice paramotor engines run a reduction unit. Belt driven or gear to slow the prop down