The whole point of paying for a child's education by everyone's admission is to give them an advantage: better grades, more sport, smaller classes, no disruption, making good connections. That is what you are paying for.
My children are advantaged by going to a grammar school. I knew enough about the system to find the tests in WHSmith, familiarise them, so that they had an equal chance against those from the private sector and those who had been tutored for two years. Lucky them.
Other people can afford to live in the catchment areas of decent comprehensives.
But I can still see that there are SOME children who may be as brainy as mine who MAY wish to apply to top universities who MAY have only got 3 Bs at A level because of the sink school they have had to attend,or other reasons, and who would prob get 3 As in the private sector.
A good education is increasingly becoming a 'game' to which only the well informed and well off are privy to the rules.
Getting 'help' with the personal statement on the UCAS form, doing interesting Gap year things (using those connections gained)are all subtle advantages that our children have.
I really don't see why a clever child from a terrible school and/or background shouldn't have a tiny bit of 'advantage' too.
I am certain the top universities are not going to squander their places on anyone who isn't able to keep up intellectually with all the others there.