If YouTube cared about anything aside from "user engagement", they could quite easily whip their comments into shape. They're not really trying.
> The volume of comments that are processed
> vastly exceeds what human moderation could possibly do
For every 500 comments, there is one video. For every 50 videos, there is one Channel with a Google user behind it. Force creators to handle the complaints about comments on their videos... an order of magnitude less work.
I've gone into this before and there really seems to be total buy-in here to the idea that these companies couldn't possibly manage to weed the toxicity off their platforms. I don't believe it for an instant. It's true only if you refuse to entertain any decrease of "user engagement". If you are willing to lose some eyeballs, the problem is manageable.
And that sacrifice, in the case of YouTube, isn't even a sacrifice! YouTube would wind up with more users if the comments weren't so toxic. Susan et al just don't have the courage to change anything.