Well, although the different formats complicate things these days, I'd wonder if, for tours at least, the larger number of first-class fixtures played back then could have partially offset the benefits of fewer tests and/or tours. For example, for tours to England (all had five tests), the number of additional (first class and non-first class) fixtures was (assuming I counted correctly):
— 1930: 26
— 1934: 25
— 1938: 24
— 1948: 27 (112 days scheduled play of 144 days on tour)
(Granted, Bradman would not have played all of these)
And the two most recent tours:
— 2013: 4 f.c., 2 T20s, 6 ODIs (and also 5 Champions Trophy-related matches)
— 2015: 4 f.c., 1 T20, 6 ODIs
So, on the fatigue question, what'd be the effect of longer tours then vs. shorter tours today plus multiple O.D. series and T20 tournaments?