Guy makes concrete suggestions, you respond with abstract rebuttals that add up to "it's too hard". All he's saying is low-hanging fruit is pluckable; pluck it.
I'll explain too; Money. YouTube make money from the spam accounts, As twitter does, Reddit too. Spam is a very profitable market.
Why else has Google not cracked down on spam accounts? It has the tech, it knows it has a problem and the best remedy they can come up with is shortened YouTube usernames? There's more to it behind the scenes.
A real example is that I worked for a business where my job was to sell email addresses gathered from soft-core pornography websites. A batch of working emails could easily fetch £500.
Reddit will sell you accounts for your "campaign" if it profits reddit and it's all the same for any big walled garden.
You wouldn't even need ML, for the majority of them.
There is actually OS tool[1] that can do this for individual creators. That tool, finds a lot of spam, that YT itself does not, and it's developed by a single guy.
So there definitively is plenty of opportunity to pluck the low hanging fruit.
But Goolge has probably 100 of PHD's developing some kind of ML, that ends up performing worse than some simple regexes, because you don't get promoted for simple solutions.
I comment pretty regularly on youtube to get random thoughts out of my head about the video I'm watching (I'm under no delusion that someone relevant will see my comment), and all the spam replies I get use unicode numbers in the username to share phone/telegram numbers. Circled numbers [0] are a favorite, though not the only ones they use. The Scunthorpe problem doesn't seem very relevant here.