The underlined; YES! But only top end power. Or via the formula, a whole lot from mid way to the top.
The bold type; Not exactly. The carb is still the carb at it's rating. The engine is pulling or consuming that 550cfm. So the carb is not smaller, just not used to it's fullest. Down grading the carb cfm size (850 to 550) is IMO a wrong way to state it and go about writing about. This wold just confuse people. It is not accurate.
The italic; YES! Because the engine is only consuming that much. But where it happens should change, slightly. Nothing to argue over. The bigger the throttle bores the less velocity.
One last thing, a carb doesn't need vacuum. The air rushing through the venturi(s) is ether done by vacuum OR the atomshpereic pressure. OR turbo/supercharger. Fuel is drawn out from the carb from the air rushing past the fuel openings in the carb.