I remember years ago looking round a rather pushy Prep where the Head was asked about the difference between his school and the more relaxed school down the road. "The parents" He said. We looked around and chose the other school, though the first might not have taken us in anyway.
I suspect the same holds true here.
Latymer, like G&L, City, Putney High and Dulwich comes around the 50th mark in the FTs more authorative and researched tables. In most parts of the country, and for many people, that would be good enough. Especially when the rowing, art, music and drama are factored in. (Just had a look at the website and the leavers destinations and 3 went to RADA and one to the Bristol Old Vic, whilst 6 went on to well respected London art schools. )
It is clear that by getting into one of the St Pauls School a child is pretty much guaranteed good results. However there is a fair amount of anecdotal evidence that this comes at cost for some of those further down the cohort. Latymer probably provides more room to be average academically but to excel in other things and come through with self-esteem intact.
Some St Pauls parents are lovely, but others are clearly very proud of the fact that their DC have been selected for one of the most academic schools in the country. This can come across as arrogance, and presumably can rub off on their DC. My guess is that this is one reason why Latymer is increasingly preferred over those schools, indeed sometimes by ex-Paulinas and Paulines.