I don't think the ad was quite graphic enough to demonstrate the benefits of two wash arms. They should have shown the bottom rack covered with pots, pans and bowls, completely blocking water from the lower wash arm and then had the upper rack filled with its usual items. Before and after pics could show the cleaning and challenge people to try that with their DWs.
Consumer Reports never saw the benefits as they only tested dishwshers with plates in the lower rack. KitchenAid did show the loading advantages when they acted like they were the first in the world to have a wash arm under the upper rack in ads for the 18 series. "Please disregard the fact that we are over a decade late to this concept."
I had a a DW with only a lower arm back in the 70s it only worked if you only loaded the lower rack with plates. It meant you had to do 2 loads the 2nd just using the lower rack for pans ect. I think it was a BOCH, built like a tank but we quickly changed it
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