You're correct, but the Australian Open in 1972-1982 in my opinion was much more
depleted than the 1976 WCT. Moreover, even if partially depleted, the WCT had still a great media coverage that year, and a big money prize too (I think we have to consider the resonance of the event): we really can't say that about the 1972-82 Australian Open (less money, small resonance).
The AO fields ->
1972: Rosewall #3, Newcombe #4, no one else from the top-30
1973: Newcombe #2, Rosewall #6, no one else from the top-30
1974: Newcombe #2, Connors #3, Borg #18, no one else from the top-25
1975: Connors #1, Newcombe #2, no one else from the top-25
1976: Rosewall #6, Roche #12, Newcombe #20, no one else from the top-50
1977-A: only Vilas (#6) from the top-10 + Tanner, Ashe, Rosewall, Stockton (but no one of them was a top-10 at the time)
1977-B: only Gerulaitis from the top-10 (maybe Roscoe Tanner, I can't find his ranking at the end of 1977)
1978: only Vilas (#3) from the top-10
1979: only Vilas (#6) from the top-15
1980: Vilas (#4), Lendl (#6), Clerc (#8 ), Gerulaitis (#9) <- but despite the rankings, you have to agree that three of these players were not grass courters and we still have no one from the top-3.
1981: Vilas (#6), Tanner (#9), no one else from the top-10.
1982: Kriek (#10), no one else from the top-10.
As you can see, this were severely
depleted fields (the only one which can be compared with the 1976 WCT Finals is the 1980 edition, but it was still worse)... on the contrary, when the field is only partially
depleted, I still give to the prestige a higher credit.
For example, Wimbledon 1972 was a major in my opinion: five from the top-10, including the two stronger players of the year... add to that the Wimbledon prestige and you have a major (on the contrary, I don't consider the 1973 edition, with only one player from the top-10: I think that the difference is evident).
Anyway I also accept who propose Los Angeles for 1972: we don't have to be stiff.
We have some numbers, but there are a lot of ways to read them: some are unconvincing, some are good even with their differences. Your tennis history is definitely good. (Let me add that I'm honoured to write directly to the one who uploaded all these historical tennis videos on youtube!)