If I ever included the USA in my discussion of Canada and Finland getting close to 100% of available talent, and I haven't found such an inclusion, then that is incorrect and I take it back. In factoring out potential to produce hockey players, I look at some obvious indices, such as the size of the talent pool, availability of rinks and other resources, hockey culture, and so on. These are rough estimates, not scientifically precise, but I believe they are valid for consideration. Its impossible to know what percentage of the talent pool has been reached, but what we do know is that talented kids have to be identified before age 16 to have a reasonable chance to make it to the elite level, and that can't be done without rinks or a hockey culture.
The US is a unique case, because it doesn't even come close to having a hockey talent pool comparable to 320 million, and more importantly, it doesn't have a hockey culture even approximating what is found in Canada and Finland. The acknowledged capital of American hockey is Minnesota. Minnesota has a hockey culture similar to Canada, but more importantly, it has the Wayne Gretzky factor. According to legend or truth, whichever applies, Gretzky's father flooded his backyard in the winter so that Wayne could basically fall out of his home on to a rink. Combining talent with a love for the hockey, Wayne allegedly developed the foundation for his talent and skill on the backyard rink. Kids in Minnesota and Moscow resemble Gretzky in this respect: they learned to skate outdoors where they had unlimited ice time, and could practice their moves with their buddies.
On the other hand, if you look at California, Texas and Florida, the hockey capitals of the Southern half of the US, where somewhere between 30 to 35% of the US population resides, there is no outdoor ice, and there is no hockey culture beyond the NHL promotions in LA, Dallas, Tampa and Miami. The vast majority of the talent pool in those states is directed toward other sports, and only a tiny sliver of the talent pool has access to expensive indoor rinks where they have to learn to skate, and develop all their skills in expensive suburban hockey programs.
If you look at NHL players from the US, the majority come from a few Northern-tier states near Canada, such as Minnesota, Michigan and Massachusetts, and production in the rest of the country is spotty and inconsistent. Instead of mass development, the US tries to isolate a few talented prospects like Auston Matthews, and then work with them intensively. The Miracle on Ice put hockey on the map in the US, but that was 36 years ago, and development has been incremental at best ever since.