About 6 months ago I ran my own little unscientific experiment with Youtube, after I noticed them promoting a certain channel that I've never watched. Nothing political or anything like that. Just a run of the mill youtuber, currently very popular with the kids.

The first week or two I was pushing the "not interested" and "don't recommend channel" every time one of the videos would show up in my feed (mind you I've never actually clicked on one and watched it and I'm a firefox+ubo user). Those two buttons had no effect at all. So I tried flagging the videos for "unwanted content". No effect either. The videos would keep on appearing in my suggestions at various places for a whole month straight.

The theory being that the channel was being actively promoted by Youtube and was thus impossible to hide. Ties in with the removal of the 'dislike' button as I believe it had the same reasoning behind it: raising the value of their advertising service.