Think this is such an interesting question. I went to Cambridge in the 90s from a state school, and I would say I did struggle afterwards. In fact, part of me thinks I've been struggling ever since. I can honestly say they were the best 3 years of my life - and maybe that sounds really sad, but also, I feel so lucky that I had that experience. I met people who I'm friends with for life, I spent 3 years studying a subject I LOVED and that I found hugely stimulating and satisfying, I was lectured and taught by some of the most respected people in that area, I had the best time socially, I was in a beautiful environment. What wasn't to love?
After uni I went abroad for a couple of years to work, and had a great and interesting time, but it took me a while to adapt and accept the people I met there. I used to get frustrated that the conversations we had just weren't the kind of conversations I'd had at uni. I got my head round it eventually, but I've had to consciously do that ever since. I still know that when I meet up with uni friends I will have conversations that I don't have with anyone else. Again, maybe that says more about me and my capacity to make friends outside of that environment. But also, I feel lucky that I'm still part of a group that is so engaged with the world, passionate, funny, intelligent, interesting.
I would also say - to echo an earlier comment, that I think I do struggle with the obvious comparison between what I've done in life and the stratospheric success and careers that some of my peers have. It is weird being in a group of people that are so successful - still my good mates, but our lifestyle paths have diverged quite considerably since we were all students together (not everyone - thankfully!). Sometimes I feel like the dullest person in the group.
So, yeah, I don't regret going to Oxbridge for an instant, and I would encourage (some of) my children to go also because I think it's an incredible experience, but for me certainly there is a sense that nothing in life since has ever matched the intensity of that time.