I agree.
Oxbridge entry depends a lot on subject. I assume that a child who is, say, in the middle of a Westminster School A level Classics or Russian set would expect to have a good chance of getting into Oxbridge. A child who is in a middle double maths set is very unlikely to even apply to read maths at Oxbridge, and indeed would probably only rate their chances of a place for NatSci, Engineering or Economics as fair.
Latymer destinations are interesting. About three years back they had about six students gain places at very prestigious drama schools, three or so gap year students were in a West End play last winter. They have a regular cohort each year moving on to well ranked art schools.
I think what I described earlier as the Chelsea banker wife ranking system is pernicious. DD was once innocently quizzed by a peer at SPGS about how she could have got a gold in a maths challenge given the school she went to was nowhere near as academic as Putney or G&L (and clearly nowhere near SPGS). The poor girl did not seem to realise that able mathematicians could exist outside SPGS. Nor that teaching could be as good (and I suspect given her subsequent questions, that anything much could be achieved without a lot of additional tuition). Who knows where this came from: parents, peers or school, but its reasonably certain some of her peers will be in for a rude shock when they get to University.
Because of the shortage of 11+ boy places in West London, LU picks up some very very bright boys and top maths sets fly. As we come towards the end of the education process, and seeing how hard DS is working at (London) University I am glad he did not pull out all the stops at school. Yes a bit of effort and a higher UMS percentage might have won him his Cambridge place. However university is a slog, and for many professional jobs you now need a masters. Internships are hard work, indeed even finding an internship is hard work (some my son is trying for, have five seperate application stages, simply to access what is effectively a six week job interview) and work is hard work too. Teenage years should not just be about grades and Oxbridge places, but gaining resiliance and social skills. Time to hang out, and learn self sufficiency and gain self motivation. One particular London problem stems from American College requirements, where the school, class placement within that school and other achievements in sport or music really matter. Cue relatively small children dragged from tutor and music teacher to sports coach, and who may reach an assumption that achievement is the only way to gain parental approval.
Neither LU nor G&L is perfect, but both try, in their different ways, to develop the child as a whole. It is never about the "best school" but the best school for the child, no matter what West London orthodoxy may say.
(Rant over...so glad we are at the end!)