Serial hybrids IC engines are simpler, because they only power the generator - no need for transmission, gears, and adjusting power through a wide range of rpm.

Serial hybrids IC engines are simpler, because they only power the generator - no need for transmission, gears, and adjusting power through a wide range of rpm. Basically generator+electric engine is the transmisson/gears. Parallel hybrids ICEs are just as complex as normal ICEs.