The data you put forth there does not suggest shrapnel was the big killer (by the way that link is to the AMEDD Center of History home page, not a specific article), but rather artillery (which is actually something I already knew–I’ve seen any number of reports that show casualty rates–particularly on the German side in the Western front, were majority caused by artillery), artillery is not synonymous with shrapnel. Many artillery deaths are due to explosive force of the exploded shell.
Shrapnel was not a big killer in WWII largely because it was no longer being regularly used. While shrapnel has become a catch-all-word for anything that explodes out at someone, it actually is named after a person (a British General from the first half of the 19th century) and specifically refers to lead balls packed inside an explosive shell. Shrapnel artillery rounds were designed to be used with a time-fuze, and would ideally detonate over an enemy position, raining all the lead balls (shrapnel) on the hapless soldiers below. That is what shrapnel is, properly speaking. It can also be extended to other similar devices which explode lead shot around the point of detonation (some grenades and land mines are made this way.)
Our troops in WWII and the enemy’s troops, when killed by artillery were usually killed by concussive force of the explosion, being literally blown apart, or being hit by shell fragments exploded out from the exploding shell. Shell fragments and shrapnel are not the same thing.
The data from WWII AFAICT is not incredibly detailed on the specific causes of death in terms of type of trauma from the artillery shell, for a lot of guys who died in the field it appears that level of data was not collected (there is somewhat more data in Korea), we do have more data of that type for guys who survived long enough to be sent to a field surgeon, as the field surgeons kept good records of the traumas and deaths. For people who survived long enough to be seen by a surgeon from an artillery shell, the most lethal injury was “amputation”, which probably means the person’s body parts being literally blown off. Concussion and shell fragments have much lower fatality rates in surgery.
There is a reason we quit making shrapnel shells after WWI–they were considered outdated and less effective. AFAIK the reason for the switch to pure chemical explosive shells is because it was concluded you can kill a lot more people by putting a big explosion onto them than by sending a bunch of lead balls flying at them from a low altitude. I believe that the injuries from shell fragments were essentially "lucky extras’< and the true lethality of artillery was in its explosive force. There’s generally available lethaltiy radii for different artillery shells in WWII, because being inside those radii essentially meant you died, from the actual explosion. A kevlar vest offers essentially no protection from that.
A kevlar vest would offer improved protection over the “nothing” they had for shell fragments, but it is unclear that that would make a significant impact. It should be noted that of people who made it back to field hospitals rifle wounds actually were the most likely wound to be fatal even with treatment. That doesn’t mean rifles were out-killing the artillery, but rather they were producing more initially survivable wounds that were ultimately fatal.