I dont disagree with the confidence remark though this has not been our experience at all.
The focus has been on learning and enjoying learning, rather than results which has suited DS fine. He has friends who are much cleverer than him but so what. He also has friends who don't star as all round academics but who have some astonishingly quirky talents. There is lots of scope to pursue interests through societies, house competitions, etc so plenty of opportunities to make your mark. The common factor for him and his friends is that they all seem very happy. His group is not particularly cool, so no sign of drugs. I would be surprised if Westminster was the only school in England who did not have a certain level of "experimentation", but there seems to be a general consensus that it is not as "druggy" as it was a decade or two back.
The only issue we have spotted is a level of fatigue from those who may have started young. If a child is having to be prepared heavily for 7+ entry to WUS, and then has to slog for Common Entrance, there is a danger that they see getting into the school as the achievement and then flop or can't find the extra motivation to then slog for the remaining public exams, and then Oxbridge entry. The fact that there are a number of really very very bright students to whom most things seem to come easily, would then be quite demoralising. If getting in is going to be a real effort, it could end up counter productive.
Our experience is that pastoral care is very strong, certainly from a day pupil perspective, where the whole boarding school house structure is in place so a house master and tutors who support pupils through their school career. Westminster is much more of a boarding school than we had expected and there is scope for a day pupil to spend a lot of time at school, effectively 6 days a week from breakfast to dinner with Saturday school and matches. Though not great, obviously, if you have a long commute, six rather than five days a week.
I dont know much about boarding other than to observe that boys switch regularly from one to the other. The availability of boarding is a real attraction for London families who have international or dual careers, so boarders are often local, some living within walking distance of the school. I dont think boarding is the easy way in any more. Indeed for sixth form it is probably the reverse.