Yes, you're completely right. If my family weren't here, life would be much more difficult for me and my dh.
It is really hard for us to say how we would have experienced our childhoods in another setting, isn't it? So I went to a same-sex school and was scared of some of the girls. I moved schools within the borough and was a lot happier in a mixed setting (probably because it was a better school, too).
I keep in touch with many friends from the second school and some from the first. The ones who were in school on time, who were encouraged by their parents to work hard, who had support at home are genuinely doing well. One is a set designer for hollywood films, and one is a bar manager (and everything inbetween from nurse to artist.) Some others have struggled, although now in our mid-20s, most are sorted.
One of the main benefits to being brought up in London for me has been the ingrained ability to rub along with different people. I can have a conversation with anyone about anything, and often do. A lot of people i met while away at university did not have that skill so innate to all my pals from home. Looking back now, nothing shocked me. I think that cultural acceptance is a part of emotional intelligence.
I apologise for being hasty and not considering your situation, but the thought of anyone feeling a London upbringing is a second rate experience (i'm not saying you were saying this!) makes me sad. I struggled at times growing up, but that wasn't because of where I was. I am really happy being here now, and hope that if you do decide to stay, you feel happy and at peace with your decision.
For what it's worth, i have had this discussion with dh. He got involved with crime as a teen. We don't want the same for our son. But on the other hand, we don't feel anywhere can offer us what london does. We feel it is down to us, not our environment to safeguard him from making poor choices.
Good luck with making the decision/coming to terms with your decision. Its bloody hard work being a parent anywhere, thats for sure!