Yup, it is simply math.
Seems like the trend has always been to reduce velocity (with maybe a slight reduction in payload from 9 to 8), maybe reducing payload and maintaining velocity would be a valid alternative approach, and reducing shot size might be a way to reduce the payload, rather than bumping up the count as diameter is reduced. If Qty9 of #00 is the established standard that is known to be effective, perhaps Qty10 of #1 at the same velocity would be much more manageable in pump guns and still over 400 grains on target. Maybe single ought has been overlooked?
And I had all this typed up before I actually watched all of the video...