Having run well over a hundred 4x400 relays at the highest level, not in the Olympics, this thread is absurd. First runner needs to be the strongest runner as they have to come out of the blocks. Last runner can theoretically run the shortest distance by taking the baton just as they near the end of the exchange or a long distance if they take the baton near the start of the zone. So if the U.S. has a weak last woman, she should have taken the baton so she would run closer to 390m than 400m.
The U.S. could have won this race if the women ran nearer to 390m. Yes, the males were slowing down near the end but the women should have started slowly at the beginning of the zone and pick up speed and ran close to 390m.
But the real problem was the U.S. 3rd runner. Vernon Norman ran slower than the lead male. Norman ran 44.40 with a running start + 7/10 that's a 45.10. The lead off ran slightly further and 44.71, which is really a 44 flat - 7/10.
Norman committed the greatest sin a 4x400m runner faces. He dogged behind his opponent without pressuring him, allowing them to control the pace; then coming off the turn, blasted home finishing with more in reserve. The team needed that reserve for the last leg. I often ran the 3rd leg; when I was coming down the home straight, my focus was on running as fast as I could until the exchange zone. If I had some more in the tank, I would signal my teammate to take off earlier so he could run a shorter distance. Or conversely, if I was dying like a stuck pig, I would signal to take the baton real early in the zone. Have some pity on your teammates, don't always take the baton early in the exchange, just because everyone else does. Most mixed 4x400m miss out in letting the women run shorter and the stronger males run further.