I understand the premise, but it's become worthwhile to think in broader terms. For example, the old Kettering ignitions had 2 moving parts, and a carb has only one. Modern electronic engine control systems have electrical dependency, hundreds of electronic components, at least one (sometimes two) moving parts (injectors) for each cylinder, another two or three moving parts in the throttle body, moving parts in the fuel pressure regulator, etc etc. Yet modern engine control is several orders of magnitude more reliable, and efficient, than old school stuff. I haven't seen any info online indicating Yamaha powered a/c reliability issues, so maybe it isn't as big an issue as one might think.
My understanding is that Yamaha included the internal reduction to allow an efficient final reduction (the transmission system). The high crank rpm apparently precludes a single stage reduction to final drive rpm in the sled. In an a/c, I expect you'd face the same issue; either accept lower max engine rpm (and lower power), or accept the extra reduction stage.
Charlie