You forget that Emily Mackay
a) had a plethora of health issues in her late teens and early 20s and has only been able to be consistent in the last couple of years
b) Attended a school that isn't wasn't in a particularly competitive conference (America East) in comparison to a lot of other conferences in XC/track (ACC, SEC) at the time she was on the team. Her high school was also in one of the less competitive sections of New York State
c) is in her early-20s, but approaching the age where development fully stops.
Katelyn is simply on one of those natural plateaus women get in their teens and early 20s. The body does not fully stop developing and changing until the mid-20s, and natural dips and plateaus are as a result quite common. Women peak in their late 20s and early 30s when their body is fully done growing and changing composition, before aging-based effects begin to kick in. Maybe give Up to Speed: The Groundbreaking Science of Women Athletes a read and then start reminding people that women do not have a linear progression the way men do and to not judge a cis woman on a male model when they give Tuohy flak on experiencing one of those natural plateaus instead of denigrating other athletes that have either entered the peak age range for women or are in the performance jump period between dips and plateaus