All good points in here. I should've added to my post that it's also a bit of a narrow premise. My half marathon PB came off of relatively low mileage (40-50mpw, maybe even a little less), but I was in full triathlon training, and I had recently started that switch and was coming off of years of 80-100mpw. I had been dealing with some injuries that likely prevented me from racing to full potential. I doubt I was in better shape off of the lower mileage but I was healthy enough to race and still had a big running base. Now, a few years later, I don't think I could touch my open running times now that I'm around 30ish mpw year round (+ 200ish bike & 20kish swim). I could come reasonably close, but I benefited in a small window of time when I had come off of the biggest mileage of my life, backed off that mileage, upped the cross training, & got myself healthy. Perfect storm of conditions. I wouldn't make the conclusion that lower mileage is the reason I ran my PB. If I ever wanted to lower my PB I would have to start running a lot more & I would have to stay healthy.
I'm sure there are OTQ types that hit their times off of a relatively low block of mileage, maybe coming off of an injury. What was their previous block like? The block before that? How much cross training did they do? It's very rare to just hit a fast time on consistently low-ish mileage + 0 cross training. &, even if someone can come up with some examples, I'd argue they're not tapped out so how much does it even matter? I don't want to say that it's not impressive to run less than your potential. Everyone has different constraints. But I'm much more inclined to get excited about the runner that puts in 100mpw for a non-elite time versus someone who runs fast but maybe chooses not to train as much, even if they have the ability to. Everyone has different amounts of talents. It's frustrating that people can do a lot less than what it takes me to run a 2:3x marathon. I wish I could run an OTQ time, but I can't. If I had the ability to run 2:3x on a lot less, I would be putting in the miles to run a lot faster. So take the anecdotes here with a grain of salt. There really aren't short cuts in running. Some people achieve faster results with less training. Often times, those people could run faster with optimized training. There might be some who can lean on quality to get to similar results. 5-6 runs/week with more workouts/less easy running. I still think that has its limits.