FYI, my opinion comes from asking the chief agronomists at several management companies what they keep their dozens of courses greens speeds at, along with several individual superintendents. And, while I haven't seen every one of their courses, I presume most have greens where the cup areas are sloped at 2-3% as is general in the industry, making it a pretty good average. I am sure there are variations.
Which is why the debate about green speeds is often hilarious, just like most things where the discussion is based on tour pros, rather than what golf in this country is really like in 2019.
Even at upscale private clubs, I think the reported or assumed average green speed isn't as high as imagined. Of course, this opinion is influenced by a story I have told here before. At one such famous club, the super was a friend of mine. I asked green speeds (in the presence of his greens chairman, who was standing just in front of the super) The answer was a confident "11+" with a wink that only I could see, clearly indicating that he (as other supers in I know in similar positions) inflated their green speed numbers to bolster members egos both in the bar bragging on their course, and on the course by allowing them putt reasonably well.