The butt of the joke is "Keith's historians" not "Keith."
They have not grown up, is the point of the joke.

Your twisting and turning on this is risible. I'm inclined to retort that it's my joke and I get to decide what the butt of it is, but I won't. Suffice to say that there is a world of difference between proper historians as a body of personages and Keith's historians as a body of personages. The former represent an august and respectable cadre, the latter a tawdry, hand picked, misrepresented and misquoted unfortunate bunch indeed. Something even mythological about them, really. Gosh, I feel sorry for Geoffrey Wheatcroft. If I have any more jokes I'll likely run them by you first, Keith, in order to get your preliminary take. If there's one thing I can't be doing with it's having to explain jokes. The moment all too quickly passes. Usually.