I doubt that Yamaha's system wastes very much power, but then, ALL motor balancing systems use moving mass and so, take a little bit of HP when the engine's speed changes. Would YOU prefer the vibrations of an un-balanced motor? Going by that diagram, its not really "wasting space" as its stuck in the middle of other components. There is (as you call it) "a moving powerless piston" running from a third crank throw in opposition to the forward twin-cylinders. You have to be talking with the Yamaha engineers on that point. My take is that its quite a good way to balance a horizontal parallel twin engine. The Flat-Four (VW, Subaru, and early Goldwings) is usually a very smooth, vibration-free engine design. A boxer twin can be fairly smooth but fore & aft cylinder mounting usually requires the barrels be higher than the transmission or the whole assembly may be just too long: 1914 ABC motorcycle. 1920s Douglas. Helios powered by BMW M2B15 engine (1920-21).