Here's a couple datasets to consider:
My drop test where I tested if heating the skirts in boiling water affected their fragility. I subjected the treatment to 20 rds and I left another group of 20 aside for a control group.
I dropped each round onto an MDF Board from a measured height of 8ft.
All of them (in both groups) broke.
This is in comparison to a punkworks test where they did the same with multiple groups of regular paint. The best paint in their group (DXS Gold), under the same conditions (except they used an oak board) broke only 15 out 20 on the first drop. The worst (DXS Triumph) had only 7 out of 20 break on the first drop.
To understand how paintballs (and FS rounds interact) with our bodies, think about the rounds impacting in slow motion. A paintball hits the surface of your skin. At the first millisecond of impact, some of that inertia is expended when the flexible ball distorts. At the same time, your skin/fat is being pushed/squished away from the impact. The longer the paintball holds together, the greater the amount of it's inertia is applied to you. This is what makes balls like monsterball, or winter paint in the summer hurt worse. They hold together longer and transfer more of their energy into you.
As soon as the rounds break, and the mass of the paint and shell spreads outwards, less of that energy is transferred into you because the mass is being transferred into a lateral direction (spreading out the splat). This is why tourney paint and, FS rounds tend to hurt less (if arriving at the same velocity).