Two different points, Jack defining most majors as the metric to compare golfers greatness is a personal opinion, it's not for him or Tiger to define the metric. It's no different than Barry Bonds claiming he was the GOAT because HR's should be the metric in baseball.
Jack's comments about the fields they competed against are based on his observations on and off the course. He's qualified to make the comments because he's played against and watched the current pro's enough to make such a determination. Jack may be acting a bit humble in this case or not factoring equipment sufficiently into his position.
Jack as an "expert" witness could testify to the quality of the fields they both played against but only give opinion on what he thought the metric for GOAT should be.
Actually Jack DID address the equipment issue. His point was that the advances in equipment made it harder for the best players to distance themselves from the rest.
Which of course makes it even more remarkable for someone to dominate to the extent that Tiger then proceeded to do.
But the poll asked for greatest: greatest <> favorite
Probably my favorite golfer in all of golf is Raymond Floyd, but I would never argue for him as being the greatest.