cf. https://www.politicalcompass.org/uk2024
Even if you consider that page biased in whatever way - it's still useful for comparisons on the same scale. E.g. https://www.politicalcompass.org/norway2025
Corbyn was (is?) a Castro-sympathizing communist. If you classify him as "left (maybe)", then I don't even want to ask what is "left" to you.
You're completely right that the Korean blues are anything but left. Not even just compared to Corbyn, even compared to European labor parties (the champagne "social democrats" in each country). Biden was more left-wing than the Korean blues. That tells you everything.
In many ways the Korean blues are more nationalist than the reds, which can't be said about basically any modern relevant left-wing party elsewhere. Another good indicator they're absolutely not left-wing.
My best theory is that he's chum with one of UK's many spy lords - that is, upper class twats with a sinecure in the secret services - and that he's trying to destroy Labour for them (and the good of the country of course). He only failed last election because the conservative party was even more self-destructive.