Bitrate per pixel is what we’re talking about. Bitrate alone tells you nothing. If you’re actually receiving a full as-advertised bitrate stream with a well-implemented compression algorithm then obviously if all else being equal then higher resolution = higher quality. But in reality many streams are overly compressed to save on their bandwidth and server costs, and often due to tech inefficiencies you won’t actually receive the full bit rate, resulting in even more additional compression losses.

Again, a perfectly-implemented, perfectly-transported stream in 720p will always look better than a dvd with a 480p video file stored on it. But in reality there are many situations where a stream is imperfectly-implemented and imperfectly-transported, sometimes to the point where visual quality worsens to below what you would get from an upscaled 480p dvd.