However, my points about Oxford and Cambridge and the complexity of issues surrounding mental health in university students can't all be resolved by the intervention of a middle class mummy.
It's a good thing no-one is saying that.
What people are saying is that given two students in the same position at the same university, an advocate who will (a) encourage them to seek support, which they may not realise they need and (b) help them navigate that support, will probably have a positive effect. No-one (here, at least) is saying that mummy will make it better; they are saying that an adult with the social (and actual) capital to help navigate it will help.
I know multiple people who within the last five years had serious mental health crises as undergraduates at Oxford. In each case, the advocacy of their parents and, in fact, their parents' private health insurance were contributory to their recovery; in large part, because parents in regular contact with their children sensed something was wrong and encouraged them to seek support.
There is also a serious problem in differing attitudes to seeking help. It is sometimes said - primary isn't my field, I don't know if this is true - that middle-class parents actively seek statementing of their children when because they realise it unlocks resources and help, whereas other parents resist statementing because they see it as judgemental and shaming. It is certainly the case that middle-class students are more willing to seek help, whereas non-traditional students (and, slightly off the topic, particularly overseas student) attempt to struggle through and then are treated badly when they seek retrospective mitigation.