Re: Were the Australian Open and French Open not considered majors in the 70s?
Bjorn Borg at 12:30 here before his final against Connors at the USO 1976: "it's the only one left, I have won the big ones: I won the French, Wimbledon, Rome and the Davis Cup..."
So you have your answer: The French was a major in the 70's. Borg doesn't mention the AO, but in my opinion the AO was a major too. When Connors won it in 1974 it was said he had won the "petit chelem sur gazon" (the "calendar grass slam").
In my opinion, back then some majors weren't less prestigious for being skipped by some big players. It's just that tennis was still being organized worldwide.
It's the idea that the AO was a major that led it to the major it is now. It's a matter of tradition and culture. Tennis was always big in Australia despite the distance.