I agree that 7% net is probably a tad high (maybe we're all suffering from recency bias), but I'm not sure I agree with your statement:

"...we need to consider that most developed capital markets have reached maturity..."

I suspect people in 1800 or 1900 ,may well have been saying the same thing, but of course there has been significant development since both those dates. How can we believe that capital markets have reached maturity when we can't even fathom what the world will look like in 40 years, or 80 years?