No serious distance runner does anything conducive to sprinting, at all, because it would all be counterproductive to distance running.
While Mo certainly works on his speed endurance over short distances, it isn't sprinting, neither is it for any other serious distance runner. But I don't think it's possible to claim that working on speed endurance over short distances is not valuable to distance runners involved in competitive races.
What surprised me in the original post was that the OP described 12.9 as a "slow" time.
It's not at all slow, all things considered, IMHO. A 13-second 100m for an athlete whose training is not conducive to a fast 100m is VERY respectable.
Consider that he actually ran slower than 13 because the timing was not FAT. With RT and proper timing he was probably closer to 13.5 ANYWHERE between 13 and 13.5, for an athlete whose training militates AGAINST a fast 100m time, is terrific.
Consider also that he is VERY highly optimized for distance running, and therefore VERY poorly equipped for the 100m. 13-13.5 was run, as you guys love to say, on "pure hate", or "pure guts".
I ask again: when was the last time you saw an Olympic 100m champion run a 10,000m? Think about the modern-era medalists, in their Olympic form:
What do you think 10,000m times would be for these guys? I would venture to guess that relatively speaking, Mo's 13-second 100m is at least as good as any of them could do in a 10,000m, and probably better.
A 13-second 100m is NOT slow. You guys have become too conditioned to hearing 9.9x, 9.8x, 9.7x, etc. Go out and try the 100m in some hack track meet, with FAT. You will feel like you're flying, and you will be lucky to run 13 seconds.