when us marathoners fail to break 210, that means the country is clean, plus there is little incentive to compete against the africans who are a mile or two ahead .... so you end up with a handful of guys that stick to track ... where they got a shot.
basically us marathoning is unchanged or worse than billy rogers - shorter - al sal eras, and realize those guys were 207 at least on a super flat course, with the shoes, and the drafting .... in their day, they had to set the pace forever .....
so all said and done, north american marathoning has gone backwards quite a bit.