Willis ran faster at the meaningful event that they each raced 100s of times. They event at which they competed.
Webb was faster at a contrived distance only Americans care about. So little was the globe's concern with the 1609.34m that Webb's agent literally had to beg all over Europe for a meet to put a mile on the schedule; nobody runs it!
it doesn't work that way
even if a guy runs ten 1500s on elite circuit & only 1 mile, you analyse each run as they are closely related distances & then compare
in '85, cram ran 3'46.3wr off total jog to bell with wide running on 1st bend of last lap which wouda been an intrinsic 52-mid/high last 400 !!!
flat-out from gun with fast pace to bell & route-1 that day he wouda run ~ 3'44+
with usual conversion of 1.08 that ->
~ 3'28-flat +/- coupla tenths
that was far superior run to his 3'29.67wr
if you have a rarely run distance but have the tools to "convert" it to a regular distance, you do so to get better measure of the man
a further example but with no easy conversion is Komen in '96 when he ran 7'20WR off suicidal opening lap & with tired legs with an arduous 13-flat from just 44 hours before
his 1500pb at the time was a nonsense 3'34
there is no easy conversion but no one here believes that you can run a 7'20 given it's circumstances off slower than 3'30, so in this case, a rarely run distance, the 3k has given some idea of a guy's 1500 ability at the time & tells us his 3'34pb was worthless estimate of his ability