"Still seems arse about tit to me."

You're right, it is arse about tit. It's important to remember that linguists don't actually *know* the origin of any word, all there is is the best theory that appears to fit the facts. It surprises me that they've not tried to claim a Greco-Roman origin for it, that's usually where linguists look when they don't know a word's origin (as if the British/Irish couldn't invent words of their own, but needed the "enlightened" classical world to show us how to speak).