You're missing the point: the opportunities were TO WIN, which is the only thing most people care about.
Yes, he won 18 because he was around quite a bit. But if Tiger wins 18 or 19 or 20 without equaling Jack's second-place finishes, so what? Almost nobody will care except the Jack apologists, because "number of times finishing second" will almost literally be the LAST and ONLY thing Jack would still have over Tiger. And it's a small thing to have, since again, almost nobody cares about second place finishes.
So no, in the context of GOAT, it's not important. The number of wins is important, the number of seconds is not.
Obviously YOU are missing the point. Tiger will never get to 18 because he doesn't have Jack's patience. I don't know how you can't see that Tiger's failure to win from behind in Majors isn't a problem for him.
Whatever. I'm done here.
JACK!! 18-14. You do the math.
You've finally said what you really mean. Jack getting all the seconds is all well and good, but to 99% of people, they won't factor into the GOAT discussion. It seems that your premise all along has been that Tiger's lack of 2nd implies that he isn't "in the hunt" as often as Jack was, and will therefore have a more difficult time getting to 19. I think that's a sound observation.