One thing to keep in mind when debating all types of rotary valves is this:
Everyone assumes the valves turn at a constant rate. There is a very easy way to vary the speed of the valve, making it open and close MUCH faster, yet slow down when it's closed.

You can speculate all you want, and even when you can plainly see the valve mechanism, you may not know exactly how it operates.

Gear driven rotary parts can turn slow for half-a revolution and fast for the other half when the gears are offset (not centered) on their shafts.