I think I saw a comment somewhere(?) to the effect that the 'supershoes':
(1) may be contributing to a reduction in the age-grade factors, and
(2) the reduction is greater in the longer distances (i.e., because one of the shoes' impact is to reduce leg fatigue, which has a greater effect as the distance is extended).
http://howardgrubb.co.uk/athletics/mldrroad20.html
At the above link, we can compare the age-grade performance between the 2010 and the updated 2020 factors to see if there actually is a trend for greater reduction as the distance extends. For example, considering 80% performance (i.e., minimum National Class) for a 60-yr Male, here are the factors for the 5km, Half-Marathon, and Marathon, and their respective VDOT's (from Daniels' calculator):
2010 80% Performance, 60-yr-old Male
Distance...............Time.....................VDOT
5k........................20:03......................49.7
Half-Mar............1:31:30.....................50.0
Marathon..........3:11:29.....................49.7
2020 80% Performance, 60-yr-old Male
Distance...............Time.....................VDOT
5k........................19:50......................50.3
Half-Mar............1:29:03.....................51.6
Marathon...........3:06:43....................51.3
Looking at the above numbers, the trend is clear; in order to meet National Class in the Half or Full Marathon, according to the 2020 Age-Grade Factors, a significantly higher VDOT is required than was required with the 2010 factors (~51.5 in 2020 vs 50.0 in 2010). This is not the case for the 5km (50.3 in 2020 vs 49.7 in 2010).