If Nike made a 4% or Next with Lunar foam and the same weight and uppers but without the plate or foam... I bet people would run nearly identical times in either shoe. The thicker foam and nice uppers are probably the biggest asset to the design. All marathon shoes produced before the 4% were all thin foamed 5K shoes. There wasn’t even one thick foamed light racing shoe until the 4%.
The Brooks, Adidas, and Nike shoes that existed before the 4% were all 10K shoes with zero cushion.
Personally as my fitness progressed over 4-5 years I ran before the shoes existed and with each new model. I don’t think the shoes are as important as good weather and a really fast course on a cold day. I’ve run more 1/2 marathon PR in Lunar Racers and only 30’seconds faster in the marathon with the Next %. I also ran several minutes slower in mediocre weather with all types of shoes.
I don’t really believe anyone running 3, 3:30 or 4 hours that these shoes really help. Anyone running an 18-19 minute 5K can’t really tell me that the shoe helped them drop a minute. My guess is their PR’s were soft. Every local 5k is run on different course in different weather. Most local 5k’s are not actually 3.1 miles.
6-7 minute miles are closer to fast jogging. You could easily lose 5-10 pounds or train harder and easily get 5-10 minutes faster in a marathon running in training shoes. Once you are running 5:30 pace no one is getting 1 minute per mile faster per mile regardless of shoes or training.
I think once you get under 2:30 maybe you can start to tell a slight difference. That is at least a decent effort near 5:30 per mile. Most runners at that point are very lean and . They probably have a few marathons under their belt to compare. I think it’s hard for someone who didn’t have a really fast PR before the shoes.... and after the shoes to have a good opinion.