With todays reverse camber is making this a grey area i feel. (if the board is sized correctly)
But typically those top shelf boards were made for aggressive, full-out, riding. Flex made strong enough to rebound a hard fast rider. Edges generally sharpen to a finer degree. Skills needed to be a bit more defined to ride.
When you throw a beginner on it. they typically arent carving at full speed to flex the board as necessary. Little mistakes are magnified and are punished by them.
Why buy a 700 dollar board? when you get zero benefit? and actually makes it harder.
a board with a flex that is rated your level or slightly above will help you keep good technique and your face out of the snow.