Yes, our frame of experience is clearly very different! Anything as thorough and time-consuming as your ideal critique, people would be quite likely to charge for, in my experience, while the kind of get-together situation I described is fairly common (but with short texts or extracts, not whole stories or even novels).
And yes, there is definitely a danger of group-think.
But I think spontaneous reactions can be valuable, too, as long as everyone involved keeps in mind the limitations of the approach. It does make the author do more of the work, as you pointed out, because they have to sieve those spontaneous reactions for what they can make use of.