Yes, 1967 and earlier was an immature stage of tennis history - when you compare the events to today's events. But so what? The players at the time could only play the events that were available to them. Are you saying that Pancho Gonzales wouldn't have been as dominant in the 1950's if they had to play events with as deep as fields as todays events? There is no evidence that he wouldn't have been at least as dominant as he was. In some ways the players were fitter then. In many many events they played, best of 5 sets, whereas today that only happens in the Slams. So nothing is there to show that Gonzales wouldn't have been the best player of the 1950's, Rosewall the best player of the early 60's and Laver the best player of the late 1960's - if they had events like today.
So Gonzales still would have been rated number 1 or co-number 1 for 8 years. Laver would have been number 1 or co-number 1 for 7 years.