I don't think it makes much difference either way tbh. Just because an area like mine doesn't have a grammar school in sight, it doesn't mean we don't have secondary moderns. Except they are called comprehensives, and it is decided based on postcode whether you need an academic education or a vocational one. Do it by means of an exam instead, and their will be little overall difference. The mc higher achievers will still get good schools, the deprived lower achievers will still get the less good, or even bad schools. The only group that would actually change would be the high achieving wc kids would get the good school over the mc average kids.
Mumsnet is not socially representative, so when dozens of posters state how great their comprehensive is, it doesn't reflect reality. It's all very well to say selecting by one exam is unfair, but selecting by postcode or religion is worse imo. But many mumsnetters either don't realise, or don't care that this happens. Its v easy to say the current comprehensive system is fairer, when for your child it just means you don't need to worry about an exam for a good school. It doesn't work that way if your child's only way of accessing a good school is by having the opportunity of an exam they would pass. Or indeed if your dc won't get into a good school whichever way you select.
Personally I'd have super selectives for the top %, and more none mainstream available for sn/Sen.
For everyone else, I've changed my mind about lottery allocation. I'd allocate funding per head based on parental wealth/ income. So the school with a large number of children from low income homes would have a much larger budget than one with dc from average mc homes, which in turn would have a larger budget than a school where many parents are relatively wealthy.
Pp funding would remain for the individuals benefit, however I'd also raise the cut off point, and offer it on a sliding scale above that. With greater transparency and areas in which it can be spent. So eg the 14yr old average achieving carer who doesn't need in school support or uniform funding could have their pp used for respite care to give them a break.
I'd also of course scrap religious criteria.