Being the best in your era tops "good-but-second best" - or even less - in any other era. Ryun not only absolutely destroyed the then world marks but at his peak in '66/67 completely dominated one of the legends in the sport of Kip Keino.
Quite apart from the improvements in tracks, shoes and spikes in recent years, I wouldn't give a cent that the top of the sport has been clean in decades. That is why modern performances seem so out of reach.