Not all dead. I think, in that count are the one seriously wounded.
Somebody loosing a limb is as useful for military purposes as being dead.
For each dead there are few seriously wounded.
I got a relative who fell from the horse in WWI and broke bunch of bones. Guess what? He never fought again!
If they killed him, it would be the same for the WWI fighting purposes.
One wounded occupies two people to carry him. One well placed round in a ten man patrol could render 30% of your opposition out of action, if they bother to tend to the wounded.
“I got a relative who fell from the horse in WWI and broke bunch of bones.”
There was a very good movie about the US Cavalry post-WWI. It was called “In Pursuit of Honor,” with Don Johnson and Rod Steiger.
What you say is more grounded in reality. However, my bet is that the original claim is even more grounded in reality—that one third of the units have been rendered ineffective.
If the number of dead and wounded in a unit reach a high enough number, the remainder is useless as a fighting force.
I saw this explained in an earlier article when the estimate reached one-quarter.