These races showed the advantage altitude-born & raised runners have over sea level runners when racing at altitude.
No matter how many months Derrick or Sara Hall or anyone else spends training at altitude, and no matter how well they respond to altitude training, they will always be at a disadvantage when competing at altitude against altitude-born & raised runners.
It will only get worse 2 years from now in Uganda where, I believe I read, the altitude for that course will be approx. 5400' . . . yesterday's race was at approx. 4100'.
That is what we learned from the 1968 Mexico City Olympics when East African distance domination first appeared. Prior to that Olympics the Australians, Kiwis, Europeans, and yes, Americans (Billy Mills, Bob Schull, Bill Dellinger, etc.) were winning distance medals.
Since 1968, there has never been an Olympics or World Championships T&F neet held at altitude . . . the lack of an equal playing field in endurance events became so apparent.
However, World XC is back at altitude and 1968 repeats itself.
The best thing IAAF can do to create a level playing field is keep the champs at low-altitude venues (under 1000m elevation).
The US men and women did so well in 2013 in part because of the bad weather and footing conditions, but also in part because the venue was close to sea level. We've seen the same on the track where Americans have become competitive with the world's best in the Steeple and 5k and Galen Rupp is ranked #1 in the 10k . . . in races all run at sea level.
Regardless of who's running, the US can do very well again at World XC . .. . . . but likely not until after 2017.