Even at lower levels, things were different then.
I was a terrible runner, AND I averaged only 40-50 slow mpw before my first marathon, a little local affair just designed to get people qualifying times for Boston (which would have been maybe 4-6? weeks later).
I "ran" (jogged and walked) in last place for much of the way, and only avoided a DFL by outrunning some old guy (who was probably younger than I am now) in the last half mile.
I was a few minutes under four hours for the distance. Terrible. But damn, in some of these big-city marathons now I'd be beating 20,000 people if I ran a time like that.