I don’t see why not. Jack is either the best or second best golfer of all time, depending on who you ask, and he was a contemporary of Casper’s. I can’t think of a better person to compare him with.
Besides, I thought I made it pretty clear that I wasn’t comparing his entire career; I was comparing a 7-year period. Of course I cherry-picked those years, and of course Jack had the better total career, but if you’re writing a golfer’s obit, I think it’s pretty significant that he outplayed the so-called Big Three for 7 years when all were in their primes.
As for concentrating on the majors, the point is that the British Open had pretty much lost its major status before Arnie and TV revived it — which is why Casper first played it when he was 38, and played it only 6 times total in his 50 years of playing majors.