The line of thinking in the other posts is exactly why I hate prospect lists. It isn’t some game where you earn points for various accomplishments or attributes.
You are a top 20 prospect if whoever is calling you that thinks you have (or project to have) more MLB skill than all but 20 players in the minors right now.
There isn’t ANYTHING, other than not being any good, that should be a disqualifier.

If Law, or Ba, or BP, or my grandma, or my cat, thinks someone is that good than they should rank them appropriately. It would be nonsensical for an educated observer to watch a player and say, “Gosh I think he will be a talented MLB player. Too bad he is too young to rank high. I’ll rank him 50 this year and then 20 next year when I am allowed to.”
That is idiocy.

I think people treat prospect lists as some sort of a game or sport unto themselves instead of what they reallly mean. It is bizarre really

While I’m on board with your line of thinking that says, in most cases rankings are used “to figure out which players will be the most valuable as a consequence of their play in major league baseball”, I’m still not buying the elimination of low-level talent. In today’s prospect world, most high level players either completely skip AAA or only spend minimal time at that level. In fact, if you look at most of the current crop of young, potential MLB stars currently playing in the bigs, few spent more than half a season at AAA. Guys like Bruce, Upton, Longoria, Ellsbury, Joba, Gomez, etc, merely had a cup of coffee in AAA before joining their big league clubs. So with that being said, minor league grooming systems for the top prospects have essential shrunk from 5 levels of ball (AAA, AA, A+, A, Rk) to 4 levels, eliminating AAA are a true evaluation level. So guys like Jennings are essentially only 1 or 2 levels away from their ultimate destination.