I see threads all the time that way "I run x high mileage, why am I slow???", but the simple answer is they're not really doing high mileage.
If one runner has 30 miles of high quality per week with 20 easy miles on top of it, that runner is a 50 mpw runner, but compare that to the runner who does 20 miles of high quality work and 80 miles of easy running.
Yes, he's hitting 100 mpw, but let's just say they recover equally from their workload. The 30 mpw of high quality will almost always trump the 20 mpw, assuming their past training was similar or not wildly different.
You hear about guys like Coe, Lagat, etc that ran really well off "low" mileage, but in reality, all of their mileage was quality (essentially). Ingebrigtsen is a high mileage runner (like El G, for milers) but really in terms of quality, hits like 40-70 mpw of high quality training and just fills in the rest with jogging (relative to his ability).
What most people (maybe only some on this board) don't understand is high mileage (of easy running) is only to allow you do the hard work, if you can do the hard work and recover with little easy running added on top, that's fine. If you can't, your personal proportion of hard:easy is off.
The amount of easy miles you run are personal, the amount of quality miles for your goal are specific and necessary.