I've seen a lot, been to swingers clubs and parties etc...
Here's my two cents. For what it's worth, I'm 6.5" (7" on a great day ) so I am slightly above "average" however, although I've never had any complaints, most of the erect penises I've seen were way bigger than me.
However, I think that's more because I was exposed to "unaverage people"... Being ENM is not commonplace, and so the people who are in that space are not part of the majority... My theory is those anywhere near or below average never show anyone but those they are personally intimate with, and inversely, those that are 1.5" or more from the average flaunt it more.