Dude, my ISTP best bud, though a toweringly excellent bloke and of no small intellect, is very often the last one to twig the meaning of a joke. And he's the one I hear most often telling me what he wishes he'd said "at the time" but didn't think of until much later, which I think is the way with many introverts...
I reckon ENxP's can tend to hog the limelight in the "witty" stakes, but only because we're quicker on the ball with the command of language, getting what's in our heads out into the open, whilst there might be as witty or wittier introverts who thought the same thing or even better, but just didn't manage to beat us to the mark.
But then that's the question isn't it? What is wit? Is it just being able to think of things? Or thinking of them and being able to say them, at the right time, before anyone else?