As a distance runner I believe you can workout and get more explosive through hypertrophy or converting IIa and IIx fibers.
My vert started at 19 inches with a max vert of 24 after a year of lifting and plyos it got to 29.5 and 34 respectively. I think you could apply this to 100 meter performance as well.
I'd be shocked if 100% of distance runners couldn't run 12.5 after a year of explosive/power training.
I'm not disagreeing that most distance guys can get stronger and get under 12.5 but 1) that's not very fast and 2) if your vertical started at 19 inches, I think you started off more explosive than is common in a distance runner. For example my vertical is about 6 inches.