Have you ruled out the regulators being the cause?
Yes. This is a physical problem, not an electrical-circuit one. It's always been this way, with the CB500 first. I was a little disappointed when Honda brought out the 550 version with the new engine size to call attention to the transmission updates, but left the alternator out of the upgrades.
It's also the reason we sometimes see a 550 that doesn't have much electrical trouble with low voltage: those got a better rotor, I'd bet on it. Every now and then I've seen the 'good' ones on cranks during a rebuild, but they are not in the majority. Mostly these show up on the 1976 - 1978 bikes, but I have seen a couple on the earlier ones (but never on a CB500 or even a 550K1/2).
