We are in Kent, so we don't have 'comprehensives' in the true sense of the word.
My DS is at superselective grammar and my DD is going to grammar in September - but almost everyone I know at our local state schools is very happy with the education that their children are getting. The only people who aren't are parents whose children may have special needs and the promises that were made in terms of support, haven't materialised.
My son is in Y7 and has done so many extracurricular activities (hockey, rugby, chess, STEM, music, drama, athletics, debating, etc etc) that I don't feel that he is missing out by going to a state school (I do sometimes feel 'guilty' as DH and I were both privately educated all the way through, but with 4DCs we just couldn't do it financially). The school has very high expectations of their students, behaviour is very good, there is very little bullying (and any there is is squashed very quickly). The other plus for us is that according to the Sunday Times, it is the 4th best school in the country for university destinations (even the Head said he wasn't sure how they calculate that, but he's v happy with the accolade and they do have a huge number holding Oxbridge offers this year). But the most important thing for me is that he is SO happy - he's thriving, is being pushed (fairly hard, but he loves a challenge) and his confidence is sky high. I appreciate that a superselective grammar isn't necessarily representative, so in the interest of balance, all of my friends whose children are at various 'comps' here and who have recently taken A Levels, are seeing their offspring heading off to Russell Group universities - but then most of us are either ex or current professionals, all have high aspirations for our children and support their learning and extra curricular activities at home. It sounds as though you are similar in your views, so if you've chosen the right (state) school for your child, then I am sure that they will thrive.
I expect some private school parents will hate this thread because it may make them wonder what they are paying for
but if you get the right state school, and are lucky with your cohort, then in my opinion, aside from the potential networking/old school tie stuff, I don't feel that there is anything we're not getting that we could be paying for......