I disagree with much of this and think he does himself a disservice by taking a clear and hard position off the fence before demolishing Corbynism rather than addressing both sides on their merits.
Can't really engage too much with the waffling on about different brands of Marxism/Trotskyism/Leninism as I don't know or care enough about them, but my biggest problems with his piece are:
1) He seems to spend his first section going into quite a bit of depth about how "Corbynites" aren't all the same and then spends the next six treating them as if they're one amorphous being with the same aims and goals as each other.
2) He spends a lot of time talking about "commonplaces", yet doesn't address the elephant in the room of the counter-"commonplaces" spread by anti-Corbynites.
3) He leans too heavily on the SWP and Morning Star as if they're considered relevant by the majority of Corbyn supporters. While I suspect a large number of readers of both are probably Corbynites, I doubt many Corbynites read either with much seriousness (data here would be good)
4) The flaw of speaking "for" the working class instead of to them is actually fundamental in explaining how Labour have reached this situation and it's been a failing of theirs going back as long as I can remember being politically conscious (i.e. Blair for certain, probably further). It's not unique to Corbynites, and arguably the fact that the Blair/Brown/Milliband leaderships failed so badly here is what allowed the room for Corbynism to be given a go by the membership.
It's also quite disappointing in that he's sprinkled references throughout quite liberally, but yet a lot of his assertions aren't actually backed up with referenced data. The best thing he has is the YouGov poll, but for a piece with so many ideas in it, he needs more data like that and less anecdotal evidence.