EDIT. I was looking at the wrong columns. Sorry about that. I've read a little of the thread and there is certainly some research. I'd never have looked at assessing the standards of sides that way. I took the lazy way. I'm not sure how many tests or series SL won in the 80s. I believe BD and Zim have won very few in their histories. I just look at the records of teams, most notably their test and series wins to prioritise them. SA beat Eng twice in series the 28-39 period and just lost another. Yet in ashes Eng won more tests. (I think they would have aced every series too but for Bradman). So on that basis I rate SA highly. Similarly the WI even though their wins were against B sides mainly though more impressive than any minnow could attain.
But I would agree about the status of Ind and NZ in both eras. Also Pakistan though they had wins against Eng away and WI and Aus at home. (India in the 50s had wins at home against Eng, though not at full strength). Overall though their records were unimpressive against the main sides and it can't be argued they were behind both SA and the WI let alone Aus and Eng both pre and immediate post war.