Amazing what people will say to try to rationalize superior talent. I mean, are the NP park kids top tier global talent? Almost certainly not; they're no Kiplimo, Cheptegei, Bekele, Kipchoge, or Geb and so on. They may not even be close to Fisher, who was clearly severely undertrained in high school and college.
But yes, they are extremely talented, and are simply innately physically capable of things the vast majority of american high schoolers are not. I have no idea how you are using Kessler as an example here. In no world is training for 1-2 years and arriving at 3:34 not international class talent. And no, it doesn't really matter if you had a solid fitness base from soccer, climbing, underwater basket weaving, or chess.
Definitely there are plenty of high-level talents that are not developed, worldwide but especially in the united states. But this doesn't really change the fact that running 4:00 or close as a junior, and well under as a senior in Sahlman's case, are indicative of top tier talent in the United states ... Definitely in the past decade alone, even before improvements in the spikes, we have seen more sub4's at the high school level, and we should expect this general trend to continue. But this doesn't really effect the level of NP's talent, which is egregiously high, and also strongly reflected by the fact that two families constitute all of their top-tier standout performances.