I think there may be a smaller group of families with multiple offers and a large group with few or none. This is a guess but as things have become more competitive there are parents who are ramping up their prep even more.
I know 2 families who have older kids that got offers from top schools ten years ago and no offers for their younger siblings (the siblings have large age gaps) - one of them was surprised as they put in a little more prep this time and said their younger kid is actually academically further ahead than the older one was at 11+ age.
The standard is very high and to be honest there is no incentive for it to change because it pushes the school's academic ratings up too. It's a bit of a vicious cycle and yes, it is at the detriment of kids.
Having said that, any children that have parents finding good schools for them are going to be turn out fine - even if they don't go to the top school's in London!
I've been lurking on this thread throughout, just chipping in my tuppence worth having just gone through the 11+ now.
Oh, maybe technology will change the game... I think training our kids to be the equivalent of an AI robot to pass these exams might change the game. The pace of technology and AI recently could make schools / parents re-evaluate what education is for - just my opinion but Silicon Valley folks don't send their kids to the types of schools we're talking about for a reason....