The selective syste doesn't fail ost dcs or in fact any dcs - the grammar schools do very well and are vety popular. You have your anger directed at the wrong target, exoticfruits - the problem is not that grammar school education is poor but that the non-selective schools are poor.
Where your logic falls right down is that you imagine - based on no evidence whatsoever - that if the bright kids were all denied selective education then alll other schools would be fine and kids would do well. in fact, if you had all the bright kids at comps, you would have a lot of disatisfied bright kids in the top streams - and those in the botto streams who the system is failing now, would still be failed.
You draw conclusions from your own experience - of someone who should have got into grammar but didn't and still has a chip on their shoulder about it - that therefore the grammar system is fundamentally flawed. But in fact your posts bely this conclusion - you clearly still think that GS are so good that you have been disadvantaged by not going. What your experience does point to is a need to improve the admissions procedures - as my post way up thread demonstrated could be done by a number of means.
In your case, I don't think you were 'failed' by going to a GS - but you were definitely failed massively by your family - as a mum of a dd who applied for GS last year, i always made it abundantly clear that the test did NOT test who she was, that it couldn't read measure the inside of her brain - that it was just a fallible test, based on her performance on a single day, and that she would do well whatever school she went to - and I wasn't just saying that to be nice. I meant it 100%.
I am shocked that any parent can let their child sit these exams and let them come away with the concept that they are a 'failure' if they don't pass. No, they have failed a single exam, not life!
I went to GS - came top in the exam BUT know I lack loads of the other skills others take for granted - the quality of my typing you can see on these posts!, can't drive, ride a bike, etc etc. I have the hugest respect for people who can do all the practical skills i can't - I just happen to be v good at exams.
You need to get over having failed a single exam at 11 - how many others have you passed since? You're a grown-up now!