That is entirely different. The drills in question are necessary to have a group of people act in a coordinated way. That requires collective training and discipline, not merely individual training. Your example is of people who trained extensively, sure, but this was not collective manoeuvres that are required for something like firing volleys. It’s also discussed in the story.
Do you think these professional soldiers trained enough to modify the structure of their bones yet not in a highly coordinated manner with each other? Have you heard of military drills?
They aren't military drills; they're legally required to practice for two hours every Sunday (IIRC), which is a world apart from coordinated formations. Notably, you can practice just fine alone, while coordination drills notably require multiple people.
Allow me to introduce the longbowmen whose skeletons adapted to being professional longbowmen.[0]
[0]https://www.researchgate.net/publication/285885888_Architect...