That is a valid question that I had to do some quick research on. My belief that the shoes are improving HS times is based on the fact I follow the CA SS mostly, and athletic.net has pretty complete data for the last decade on top performances. A simple way to measure this is to look at the 25th best mark for a given year ( to adjust for outliers). Distance times were pretty stagnant from 2014 until last year. Last year times were a little faster than ever in just about every way to measure the top 25 (all grades, each individual grade). This year they are as well. You could try to say that was population increase, but my understanding is track and field participation as a whole is not significantly higher than before. So did nutrition, training and coaching just get better these last 2 years. Well, as you suggested I looked the shot put, and these last 2 years have a 25th best mark that is worse than any of the non-covid years for a decade. The discus also has worse marks than through the 201x's. these last 2 years. So what is the explanation for those getting worse? Nutrition is worse? Training is worse? The 100m and 200m times look stagnant. Better than some past years, worse than others.
I agree that the airlift compression is a ridiculous comparison. Looking at the data, it looks like 1-2 seconds improvement in the 1600m, and about 4 seconds in the 3200m directly tied to the last 2 years. What changed specifically and only in the last 2 years? And why is it only distance running?