Popular forum software (discourse, phpbb) have good mechanism for comments moderation. For example a comment from every new user can require approval before it becomes public. YouTube doesn't seem to have such mechanism, so the moderator would need to continuously monitor the comment section.

Youtube has this functionality:

https://support.google.com/youtube/answer/7284070?hl=en

Yeah but also your moderators are actually just users who don't know anything about moderation, and you didn't tell them at any point that they have to handle moderation duties.

So you turn comments off and tell them if they do turn it on, they have to moderate the comments.

Does YouTube even provide tools to let people do effective moderation nowadays? Just telling content creators that it's essentially their problem now can't be the whole solution. This reads like the typical Google response of leaving the people that fill their platform with quality without any useful feedback.

YouTube moderation tools were abhorrent last time I tried them.

Yeah, and most of the channels I follow have 1-5 people producing them while sitting on millions of subscribers and tens of thousands of comments on most videos.

It will just kill small but successful channels because of the sheer amount of moderation to do.