Just a bit of a rant really, but unless you are wealthy enough to a) go private b) pay a massive premium to buy in catchment or c) lie about your religion (or actually be religious!) then do you have to accept it's basically a complete lottery?
We've still got a couple of years as DD1 is in Year 3 but we live in a very small house which we have extended as far as we can and really need to move in next year or so. We'd like to stay in our area of south London so the kids can carry on in primary and we're close to grandparents, DH can cycle to work in town etc. etc. However there is no way our budget will extend to a house in catchment for any of the outstanding schools in our area and I've heard of children in our street getting placed in schools the opposite end of the borough (1 hours journey during rush hour on 2 buses).
My only consolation is that none of the schools are really awful but it seems a bit rubbish that DD might have to travel for over an hour in London (travelling past plenty of perfectly good schools which you can only get into if you can afford a £800K house)
OP, I understand your frustration, but the reality is that we're actually luckier in London than elsewhere, statistically. I know that doesn't help your worries, but remember it could be worse.
You might consider (if you can hang on in your current home for a few years) selling your property before secondary application and then renting for a while in the catchment you want. Once you've been accepted in the school of your choice then you can buy again in a slightly wider area.
Renting then moving to outside the catchment can mean your DC2 doesn't get a place (the automatic allocation of DC2 into DC1 school has gone here. Even when the allocation was a sureity it was if your DC were IIRC less than 4 years apart)
Schools change, we have 2 Secondary Schools about equal distance, one of which I used to hear "Don't send your child there" but it has improved with a new Head. It's reputation though will live on.
And it goes without saying, outstanding schools can decline too.
We're in a similar position (se London). Our area is excellent for primary schools and has two of the best grammars in the country....but the local comp is beyond awful. It depresses me just driving past it. If dd1 is not clever enough for the grammar (super selective so not much hope) then we will be looking to move in next few years. Can't afford nearer into London or nearer to local schools with better reputations (same size houses cost £200k more in relevant catchment areas) so we will consider further out in kent if necessary. Means we will be further away from family and friends, commute will be longer, but education is more impt to us. If the comp were good or even adequate we would stay put and get on with it, but I honestly can't see myself sending her there if it would depress me to have to go there every day.
Cast your net wider OP, there will be other compromises to be made, but you might be able to afford a bigger house nearer to a decent school for both your DC?