[oblio]

"Significantly better" is a stretch.

The comments got much better after Youtube added user ratings. Hardly "ML". I'm guessing they added ML later, but I haven't noticed any difference, to be honest...

And by "much better" I mean they went from amoeba level to early multi-cellular organism :)

[azernik]

They are likely using those user ratings to build a model of what kind of comments bad users make.

[oblio]

Most of the bang for their buck was when they used a plain old sorting of those ratings. That already hid a lot of the sludge. The ML stuff is just a minor optimization compared to that.

Everything is just my opinion, of course, they're probably following a bunch of metrics I don't have access to and which could prove that the ML effort was worth it.