It is a bit disingenuous to compare video codec quality using stills. One can simply choose a key frame (= no temporal compression) to compare, and they'd like

It is a bit disingenuous to compare video codec quality using stills. One can simply choose a key frame (= no temporal compression) to compare, and they'd likely be identical regardless of how well the codecs compress motion in non-key frames. (Not sure if the video clarifies this point since I cannot watch it right now.)