I'm not sure your description matches the video.
The video doesn't seem to be so much "why are tankies like that?" as "all socialists are tankies and that's a good thing".
A lot of things he said just seemed to be completely wrong. For example, he says that nobody ever said that Stalin or Mao did nothing wrong, but those are fairly common sentiments among the online left - you don't have to look very far to find whole subreddits dedicated to those ideas.
I'm not sure whether he was attempting to defend Castro or Kim when he compared them to each other, but in any case, both should be condemned.
He's probably right that most far-leftists (newsflash for all the socialists out there: you aren't "the left", you're just part of the left) are Marxist-Leninists, especially globally. But it isn't "Western arrogance" to then say that Marxist-Leninism is bad. If anything it seems to be patronising to not hold people to the same standards. "It's OK that you're evil because you're not white uWu" is racist in multiple ways.
Then there's the "well if it's not OK to support the Chinese government then it also shouldn't be OK to support the US government", which is "I'm 14 and this is deep" stuff. Like, yeah, sure, the US has done bad things. But the US is a liberal democracy (not a perfect one, but nonetheless), while China has been a one-party state since the war. If you don't like your leader in the US then you can elect a new one, with elections being held regularly and resulting in big changes in policy. China is an oligarchy ruled by a ruling class for a ruling class. There is no way for Chinese people to influence their government short of breaking into that oligarchy themselves.
I skipped ahead a bit and... this guy is literally talking about his "critical support" for Gadaffi and Assad. He blames the Syrian civil war on "US-backed militias", and not, you know, Assad torturing children who graffiti, the Syrian occupation of Kurdistan, or ISIS, all of which were more significant than the rebel groups backed by the US (who famously turned out to be basically useless in the actual war).
And then he ends his "why I support Assad" talk with "liberals uncritically support the US!", which firstly philosophically if not logically contradicts his earlier claim that nobody uncritically supports Mao, and secondly is just laughabe, isn't it? Like, who are these liberals who go around defending the Trail of Tears, slavery, Japanese internment during WWII, the bombing of Dresden, the Vietnam War, the war on drugs, the immigration policy of Donald Trump, and so forth? Even, say, the Electoral College? Basically every liberal will have criticisms to make of the US's human rights record, and if they're not American then they'll also be able to criticise their own country.
I guess this was useful because it exposed me to what a tankie thinks, but it's far too sympathetic to Marxist-Leninism. It isn't a critical analysis of what leads people down the tankie rabbithole, it's "tankies are good".