I suspect that number is shading the truth to make today look better.
Wikipedia has a list but no counter so I did it with a view to speed rather than 100% accuracy. In a very quick rough count I see 555 Army Generals, 89 USMC Generals, and around 230 USN Admirals.
That is around 950. There may be a handful of Coasties or whatever. Then there are two other factors to consider. This list includes those who were Generals at the beginning of the war. George Marshall conducted HUGE numbers of firings at the beginning of the war of the ones he thought were two old, not a good fit for the fast moving and learning and expanding force he was planning, or otherwise undesirable. But all of those were still counted on the list.
Second, the list includes the ones who did not complete serving the entire 3.8 years.
In reality there were only around 1000. So the ratio is over twice as bad as you even posted.
This site is discussing that we lost 40 dead Generals in WWII. (Something else that no longer happens) And they said “out of about 1100 who served at SOME point during the war.
This ling
And I forgot, that count included around 100 USAAF. They were not included in the US Army list.