I found the article convincing. When the throttles are ganged, there should be only one slider. When they are not ganged, there should be a visual indication

I found the article convincing. When the throttles are ganged, there should be only one slider. When they are not ganged, there should be a visual indication of the propeller speed differential. Perhaps a horizontal bar above the throttle sliders that grows left or right according to the consequent turning moment.