You didn't even look at her times correctly. She ran 52.64 in the 400 and 4:41 in the 1600.
It's worth mentioning the Mu raced SIGNIFICANTLY MORE than Willis did in high school. Mu wasn't untrained, she was just trained as a sprinter. But what we saw this year was Mu has struggled to maintain that sprint speed as she increased her endurance training.
Meanwhile Willis even has a 17:46 cross country 5k to go with her 52 second 400. Her training was more balanced (and not overdone) and I think indicates a more linear career progression.