I actually think that this problem you discuss (which events were the most important at a given time) is the main reason why it's so hard to write an all-times list of the best players (and why the plain Grand Slam total-based list is a ridiculous way to do so)...
As for the Aus. Open, given the geographical and time of the year factors, it could only be a great event when:
a: there were great Aussie players.
b: Australia won the Davis cup, because then another team (usually the US) would challenge them in Australia, and then stay to play the tournament.
That was the case at diverse times, the 1910's (Brookes & Wilding Era), and mainly from the 50's to the late 60's.
I agree it became a great tournament, almost equal to the other GS with Wilander's victories. I'm pretty young and doesn't remember this era, but reading the articles from this period, I have the feeling that Edberg's win in 1985 was considered almost as big a breakthrough as Becker's at Wimby the same year.
The French, on the other hand was always a big tournament, from 1926 on...Maybe it wasn't very prestigious indeed for american players for cultural reasons, but for the great clay-courters it definitely was more important. Rosewall won the French pro (a clear copy of Roland Garros for the pro tour in the 60's) on clay 6 times and was considered one of the best players of this time, even if he was often beaten on gras at the US pro and Wembley by Gonzales or Laver. An inaccurate look at the firt Roland Garros Open fields could draw a wrong picture, because from 1970 to 1973, the field was totally depleted due to conflicts between the WCT and the ITF, evoked earlier...Basically, during these years, there were only 2 Grand Slams, Wimbledon and the US...After this brief period, RG became a big tournament again when Nastase, No1 in the world won it in 1973, and when Borg, supreme on clay, started to become an all-court player... At Mac's time, RG was clearly a VERY significant tournament.
Coming to the WCT Finals...After the creation of the ATP in late 1972 and thus the end of the conflict between WCT, WTT, NTL and ITF, Dallas was never as big as it had been. In today's standard, it was a bit like Key Biscane: the biggest non-Grand Slam tournament. In 1970-1972 it was very important, as well as the whole WCT tour, for one very good reason: the prize money was so much bigger... Players are human, and even if they're sensitive to the prestige of the Grand slams, they prepare better for the bigger-prized events, and that's why even the Wimby and US results cannot be considered as significant in these years as after that.
Look at 1970, a year when John Newcombe was named No1 in the World... He won Wimbledon and 3 tournaments. Rosewall was Wimbledon runner-up, won the US and 5 tournaments. Laver was miserable in Slams, losing in the 4th r of both Wimbledon and the US...but he won 13 tournaments (that is almost all the WCT tournaments), and dominated everybody, being 3-0 against Rosewall, and 5-0 against Roche...Who was the best? And can you think of a player this hot performing so poorly in Slams, not reaching even a QF? That should tell something about the preparation at this time...
I hope this wasn't too boring, I just like a little tennis history talk from time to time thats 'all
PS: Fabrice, I like your " Mac should have won this and that" theory...The Borg should have win at least 3 US Open and 3 australian if he had played them and would have 17 slams...
Plus, "if" some things were fair, for example, Mac would never have his celebrated 4-years-in-a-row-as-number-1, because in 82 he won nothing, though Connors made the Wimbledon-US double, and Lendl won 12 tournaments and was US runner-up...Mac should be No3 in 82!!!