One thing to consider about the "As far as I can tell those buttons aren’t connected to anything on the back-end." idea is - if a new channel or video comes out

One thing to consider about the "As far as I can tell those buttons aren’t connected to anything on the back-end." idea is - if a new channel or video comes out, the algorithm might not know its undesirable to people in your cluster until enough unlucky people in your cluster is served that poor video recommendation and hits that button, at which point the ML has sufficient labels to start avoiding serving that video to people with similar preferences to you. But there's an endless amount of new content, and new content has a period before its properly labeled and sorted into the right filter bubbles, so you will likely never get to a world where you don't have to see that stuff.