In addition to marketing, Kerr seems to be trolling. During the podcast, he didn't lead with saying the mile WR is harder than the 1500m WR. His first comment re: the difficulty of the mile WR was, "It is the hardest world record right now and the oldest world record right now in athletics."
Kerr was factually incorrect about the mile WR being the oldest (El G broke the 1500m nearly a year before he broke the mile WR), and he didn't qualify his opinion to only distance records. If he was referring to all track events, I think Bolt might like a word!
When he was talking about the mile vs the 1500m, I thought Kerr would try to argue that the mile WR is harder to break because there aren't many opportunities to race it. I don't know if I would buy that argument, but I might consider renting it. But Kerr didn't say that at all. Instead, Kerr's argument was:
- the mile is an extra 109 meters, and "it is frustratingly annoying to work out that nine meters"
- there are more variables in a slightly longer race
- it's harder to start on a bend than it is to start on a straight
That last point is actually solid, but I don't think it's enough to outweigh the reality of 54.93 laps vs 55.46 laps.
I think where his argument really falls apart is his belief that running 3:27 in Paris was an indicator that, "it's not out of the realm of possibility that I could have done it [break the mile WR] that day." Even after taking into account the rounds and having to sleep in uncomfortable beds while in Paris (reasons Kerr gave for why he thinks he can run faster than he did in that Olympic final), saying 3:27.79 indicates that you can break the mile WR isn't good support for believing the mile WR is harder to break than 3:26.00.