For those unfamiliar with British political discourse, the term "Tankie" is often used in British left-wing circles to refer to supporters of Stalin (including his approach to political change through violence), and is usually used in contradistinction from "Trots" (= follower of Leon Trotsky's -- who disagreed with Stalin on several things, but not on the use of violence). Whatever one might think of Corbyn and his supporters, "Tankie" is probably not as exact as might be desirable.
tbf whilst I completely agree the "tankie" label doesn't fit Corbyn and his average supporter particularly well, one of the more interesting properties of Corbyn is his ability to maintain very good relationships with both the "Stalinist" and "Trotskyist" factions of the British radical left (who tend to hate each other and have little more regard for the Labour Party)
I think the "tankie" description is pretty fair when applied to likes of Seamus Milne and Andrew Murray, though of course Milne stopped being the Guardian's comment editor to work for Corbyn and Murray hasn't written for them since 2013.
"Tankie" has (on the internet) become a term that the center-left uses to refer to the left. It's replacing "alt-left" and even getting traction in some circles that identify as "socialist."
Not related to his Corben pieces but Owen Jones is probably one of the weakest journalists I've read. It is clear his articles get clicks because he keeps being featured but I cannot stand his pieces.
