Yep, your correct Zenoah's do have double cheek crank's. My mistake...

There are many engine's utilizing a double cheek design. Obviously there not all using the same balance factors or ratio's. As Diablo mentioned tune-ups play a factor. Additionally ignition system's contribute here as well. The smoothest single cylinder will have a properly matched carb, low friction loss HP numbers, auto advance/retard ignition system and balance factors that match the application. I believe the rigid rotating assembly of the double cheek crankshaft design allows more energy to be converted to usable power, this is realized via the transition, rpm, torque and smoothness.

It's much like the real world of automotive engine design. There are many aftermarket components offered to enhance performance. The right combination of these parts and hands on massaging creates a high power engine, the wrong combination creates an engine with less than desirable attributes...

DA's new 50 does utilize a cantilever crankshaft design... I assume weight and cost were a factor. The 50 makes respectable power. The rpm numbers I have seen are comparable to other engines in this class, if not less...