I think I agree with the message here. We have to be careful assigning numbers too liberally.
I think that those pro majors do matter. A lot. And knowing who won and which ones is important. But counting them up and comparing those totals with those of the present eras is no doubt misleading.
However these very results, the pro majors, are still useful in order to illustrate the extent to which some players dominated their respective tours. For example, we know from looking at the results of the majors in 1967 (whatever they may be) that Rod Laver ruled tennis.
I would also like to remind that the so-called 'pro majors' were not always the same three or four events from year to year in the 1960s. Yes, typically we would look at the US Pro, Wembley and French Pro, but participation in these events did vary depending on the year. Although less so than in the 1950s.