God @blueshoes, the contempt dripping off you. You really do revel in bringing the stereotype to life don't you?
If you were to look abroad as a result of progressive changes in education policy, I daresay the country would survive it. AFAIC, it isn't about bringing in astonishingly gifted parents like yourself to state PTAs who will save the failing institution from itself hmm. It's about removing a parallel system that poaches the best teachers. And no I don't blame the teachers. They went into teaching because they want to teach; this is much easier to do well at a private than at a state school (in general, I hasten to add, before all the fantastic state school/shit private school examples start again).
Add a massive salary increase and private company benefits and frankly you'd have to be saintly to resist (some teachers are saintly, mind, and stay in state schools because they believe - rightly in my opinion - that the impact they can have there will be of far higher value even though it will be harder to achieve. Like NHS doctors who could be working privately but choose on principle not to, these people are my heroes).
It is not necessary to go into stereotypes or namecalling. We are having an adult debate on this thread. Thankfully, my advocacy on behalf of the students is not required in your eyes. I daresay other posters have mentioned engaged parents as one of the benefits of a system that removes choice in education.
The parallel system you described above is exactly the interaction that goes on between the public sector and private sector in all walks of life. Very talented people still work in the public sector, as I am told there are great and better teachers in the state sector. At the risk of stating the obvious, this is a capitalist society. Both sectors will improve from the competition.
Private schools do not enjoy teacher job stability just because a place pays more or has better benefits. People who leave for better pay/benefits/easy life are the ones more likely to job hop anyway and so private schools could be setting themselves up for a high turnover by using such bait.
The quality of teaching is one of the areas I am least satisfied with at dd's private school, though it suits her in other ways. It is the usual churn of teachers, teachers occasionally not turning up for lessons/cover, maternity, leaving part way. Private schools don't have some special respite from the usual HR-type issues in any organisation.
You are not missing out that much in the state school.