Not so. Very ordinary runner.
At my best I was a 2.45 capable, that harboured ambitions of breaking the magic 2.37. Never got close.
I ramped up miles for a season and just got slower. I had more DNFs that year, than anytime before or after, All my best times were off a 5 day 50-60 mile programme.
No junk miles at all. All but the very long were faster than marathon. Two days off saw improvement, the quality sessions became higher quality. Also, tapering I found it was better to actually increase quality but substantially drop volume. So the 9 rep session tapered to 5 but faster etc.