Errol our grammar, despite being superselective, offered no Latin or Greek at GCSE, no Classical Civilisation either, and nothing again at A level, even as a twilight thing. Absolutely correct: the numbers taking A level languages (modern or classical) is tiny compared to other subjects and heavily weighted towards the independent sector. You've already stripped out huge numbers being able to apply.
At Oxford there is of course the option for state school applicants to learn Latin/ Greek at very high speed in the first year of the course, with 9am classes five days a week, alongside the other stuff like history, literature, art etc. Big old filter there too :)
I don't want to do down the three DC of mine who read History at Oxford but having been able to compare their interviews with DD4 (Classics II), there really is no comparison. The bar for language skills was exceptionally high, whereas for History you merely have to be capable of analysis and making links and show a relatively interesting mind.