The nature of golf is such that it doesn't lend itself to simple statistical analysis, as is often offered on here.
There are a limited number of events, and very few meaningful events (ie majors), compared with the number of pro golfers out there. When you add in the statistical dominators (Jack, Tiger, etc), you can't meaningfully compare across eras. There simply aren't enough samples.
Simplistically, if Tiger plays 20 years, with 4 majors each year, and wins 14, that only leaves 66 other majors to be won. You can't have 5x as many different major champions among the rest - there aren't enough events! And one other great player - oh, let's call him Phil or Tom - can completely skew the "other guys capable of winning a major, as evidenced by other guys winning a major" evidence offered.
Someone with more time on his hands might be able to compare the relative rankings of the guys who won - in other words, coming up with some sort of average ranking of the guys who win majors. If it was 15 during Jack's time and 50 during Tiger's, that would imply a lot more guys capable of winning majors.
But that depends on accurate rankings for those other guys, and I doubt that really exists.
In the end, people believe what they want to believe.
And anyone who believes the fields during Jack's time were anywhere remotely close to the fields during Tiger's time is simply delusional and trapped in that great coping mechanism, denial.
And anyone who believes the fields during Tiger's time will compare to the fields of the next Tiger, in 10-20-30 years, is equally delusional...
Likewise, there is a lower bound to how low you can go, so all those discussions about 58s, 59s, 62s, 63s, well, they all have to be assessed individually as well. And that doesn't even take into account weather, course set up, etc, etc.
Maybe Brent Hutto could explain it better to everyone, if he still posted on here....