I don't assume much of a reliable correlation; but it doesn't require much. Once you have found a likely few doctors, it is worth finding out if a lot of people hate one of them -- particularly if they explain why. It's basically a very cheap way to filter out potential problems. If I felt that there was a strong correlation, I would have recommended starting with the Google reviews -- after all, Googling is much more time expedient than talking to people.

For context, of the few doctors I sampled on Google review, I found none of them to have anything significant posted in their review. The worst I saw was "receptionist was very rude!"

Given two or more okay choices of doctors given by friends and acquaintances, I think that it is fair to apply this sort of filter, even if you have weak evidence that it is effective. The worst that will happen is that you make the other good choice, rather than the good choice you would have made. The best that might happen is that you avoid an unpleasant experience (well, the best is that you lower your chances of dying through physician error). This calculation may change if you have only one doctor under consideration.