Thanks for your post.
To my best understanding, low quality page is always the combination of high bounce rate + high exit rate WITH low time on page (seconds).
High BR and High exit rate don't necessarily mean that the user hasn't gotten what he was looking for. If he stayed minutes on that page, he probably received an answer.
But if that page has these 3 metrics attached to it, it screwed and must be improved or nuked.
Correct me if I am wrong.
I agree with you that it is not about quantity anymore. Google is looking for tight quality, not mountains of crap.