When I graduated, ahem, a few decades ago, the main difference between Oxbridge (maths graduates) and non-Oxbridge, specifically the Cambridge Maths Tripos, was that is was teaching the same content it had for the previous decades, whereas the maths courses at mine, and other 'Russell Group' universities had been dumbed down for the first couple of years. You could reach the same level as previous graduates by the final year, but you had to take a new additional course.