My opinion: Cheserek is the best ever....period. Rosa would probably be second but he wouldn't run away from the best guys in the 70s and early/mid 80s (Ostalazaga, Gregorek, Heffernen etc...) Gregorek in particular-never lost a XC race and probably didn't lose a track race junior and senior year (won the golden west meet in Cali his senior year)... Always did just enough to win.
My comment about mileage was a reference to the fact that today's runners are only at or about where we were in the 70s. Diet is better and coaching is generally better. But mileage is way down. We ran 100-110mi per week in HS in August. Slow and on grass or dirt to minimize the wear and tear. That sort of pre season base building is what really makes a difference. It is also higher risk i.e. i missed every third season in HS and College due to injury. It won't enable an untalented plodder to beat a superior athlete but most, not all, athletes will do better i.e. will run faster in their career, on a pre/early season high mileage training schedule.
My prescription for most runners (life is a bell curve...what works for most won't work for all):
Jul Long Slow Distance (LSD) 50 building to 70mi per week
Aug LSD 90-110mi per week w a 4 X 2 a days (AM/PM) i.e. 5mi AM, 10-12 PM
Sep/Oct 70-80Mi per week, w 2 hard interval sessions per week, race through early season meets...a couple of 2-a-days a week.
Nov 60 mi per week, short/sharp intervals, rest and PEAK for States
I know...no detail. But very generally speaking, this is what the best teams in the 1970s were doing.