I think the more amazing thing is that ANYONE has run faster. And keep in mind his time was with 1.5 seconds of the then-WR. He was a once-in-a-lifetime talent.
Had Ryun not had mono in 1967, I like to think the Olympics would have gone differently and then maybe so would the next several years. He clearly was not the same runner after that (just like Ovett was not the same post-1981 injury).