I guess we're in extremely different talent pools, but I've seen this proved wrong more times than I can remember. Some stay dominant and some get passed by.
Success at 12 in no way guarantees success at 18. A little thing called puberty often kicks in.
A little thing called work ethic too. My kid played with two boys at 13U who were big, strong and quite gifted. Neither was a perfect player, but both were very, very good. Of those two, one is out of the game, and the other is a top HS player, plays for a regional powerhouse showcase team, and has a verbal to a Pac12 team. The difference is that one kid rested on his natural ability and resisted efforts from coaches help him get better. The other is coach-able, works his butt off to get better every day, and then works some more.
The work ethic thing I get. But the dominant players fading a lot... just never seen a lot of that. But again I may have a different definition of dominant.