AFAIK you can do that? Hit the menu on a video recommendation, "Not Interested" -> "Tell Us Why" -> "I'm not interested in this channel".
IMO, though, blacklisting has been mostly proven to be insufficient. If you block, say, noted chud Sargon of Akkad, that doesn't mean that another half-dozen "Rationalist" "Thinkers" Who Just Happen To Be Chuds won't be recommended to you as well.
Not sure if my experience is typical or not but that hasn't helped me one bit. When I tried the various signals you listed, that just seemed to encourage YouTube to show me even more videos/channels similar to the ones I wasn't interested in. It seemed to be more a signal of 'hey, this person will help us identify more videos like this' than 'let's not show this person any more of this type of content'
allow channels to categorise themselves (which I believe already exists but is underutilised?) and allow users to express positive or negative interest towards categories. There is little incentive to self-categorise incorrectly as it would lower your visibility to those who want to find you.
If you are getting suggested these things it's because people with similar viewing habits as you watched them. I get suggested riposte videos to such content without ever seeing the original "bad" video. I'm assuming this is based on my own habits on the site. I would prefer getting neither, but here we are.
To claim that blacklisting would be ineffective because there is always more trash is disingenuous. If everyone blocked (e.g.) PewDiePie, surely they would get less YouTube talking-head content.
It's like saying that we shouldn't/can't avoid candy because people are always making new candies.
It's well-documented at this point that YouTube's recommendation algorithms enjoy feeding fascist chuddery to people who like things like video games or history, yeah. But I didn't say you shouldn't do it. I do it, because one fewer garbage channel is one more chance for something less garbage. But it certainly seems like it's bailing against the tide.
I second that personal blacklisting is insufficient.
I did just that, clicked on "not interested" -> "tell us why" -> Not interested in this channel"
Yet I'm still getting video suggestions from "Charisma on Demand" and the like.
Also this mechanism doesn't account for changing tastes.
I was one interested in a certain gun channel, but after a shooting and particularly deft comments about it by channel owner, I decided to take up interest in literally anything else.
Yet the videos from it and the like followed me around for about a year.
That 'feature' does nothing. I've tried everything, but getting youtube to stop suggesting to me videos from Jimmy Fallon or Conan Obrian or any of those other 'lame obsolete-format "late night" shows for tepid boomers who miss Johnny Carson' seems to be totally impossible.
Video Blocker extension for chromium and firefox keeps me sane on YouTube. It is surprisingly quick to block the main offenders and have actually decent recommendations on the sidebar.
