I agree you can't generalize. I went to a dreadful catholic private school up until 8th grade and a very good public high school. My nephew goes to the same catholic school now because my SIL is afraid of public schools. He's getting a lousy education that, while not extremely expensive, isn't cheap either. There are about 30 kids in a class, there is nothing in the way of arts, extracurricular activities, etc. There is lots of religion and english taught, but about zero math and science, just the way it was 35 years ago.
There are a couple of very nice private schools in our area. They cost $15-22K per year. The campuses are gorgeous and there are all sorts of enrichment programs. That's nice, but I just don't see it happening in my family any time soon.
Actually, even if we had the money, I don't think I'd send them there because they are single sex and I don't want that for my daughters. I also don't want them to be in such a very homogenous environment.
Likewise, the public schools in my area vary quite a bit, too. There are some that are lousy and some that are excellent. We are, on the whole, quite happy with the school dd is in. We picked our house based on the school district and it's been a good choice for us, even though we could have gotten a nicer house in a different neighborhood.