Well the one mile and marathon stats pretty much prove OPs point

Only because he picked 50th percentile. If you'd sample 75th percentile I think for most sports it'll hold pretty true to the 80-20 rule for mastering something: 80% of the result comes from 20% of the investment, and to eek out the last 20% of result you'll have to invest 80% more effort / time / money. Especially the last few percentpoint gain require an inordinate amount extra.