It should be emphasized more that Fisher is still only 25, with a spring birthday. All of the modern day American greats who have been named in this thread had their greatest international championship success at ~26 or older:
Rupp - won first Olympic medal at 26
Lagat - didn't become American until he was 29
Chelimo - won first Olympic medal two months shy of 26
Meb - won Olympic medal at 29
Jager - won Olympic medal at 27
Centro - won Olympic gold at 26 (two months shy of 27)
Impossible to say at this point if Fisher will wind up as the American distance GOAT, but his career is off to a great start. Based on their events, he is most comparable to Rupp, and his career up to age 25 stacks up very favorably to Rupp at the same age (and both have spring birthdays, which makes for a fair comparison):
Rupp at age 25: 3 national championships, 13th at Olympics, 7th and 8th at Worlds, PRs of 3:39.14, 7:42.40, 13:06.86, and 26:48.00
Fisher today: 1 national championship, 5th and 9th at Olympics, 4th and 6th at Worlds, PRs of 3:35.53, 7:28.48, 12:53.73, and 26:33.84