I'm rewatching the series Band of Brothers. Its alluded to from the episode "Replacements" on, but directly voiced by the character of Frank Perconte in the episode "Why we fight" that replacements both got Toccoa men and themselves killed quicker. A quick internet search showed that, for example, in Italy in 1943 only 34% of line infantry had been trained with their original unit in the states (the rest were replacement soldiers from "repple depples" or replacement depots). https://www.defensemedianetwork.com/stories/the-u-s-world-war-ii-troop-replacement-policy/

The fact that the individual replacement system was abandoned in subsequent wars by the army supports the assertion that it was ineffective, but doesn't answer whether a replacement or "original" member of the unit had a longer life expectancy.

Thanks!