They were what we call "experts". Real ones. And Roosevelt, for all his other faults, was smart enough to let them run the show. The aptly named Robert Strange McNamara, for all of his exalted three years of service, was absolutely NOT an expert on running a war. Lyndon Johnson, for all of having served as a Naval Officer reaching the "high rank" of Commander, was even less an expert on running a war.
Roosevelt let the experts run the war.
Johnson ran the war with his own utter lack of expertise.
My Dad (USAF) introduced me, at a very young age, to the saying “nothing is too good for the troops”. It took me a little time to catch on to the double entendre ...
His point was more that the experts weren’t running the war.
Eisenhower? Nimitz? MacArthur? Groves? Not experts?
Part of the problem with the Viet Nam war was that the politicians (Johnson, primarily) DID NOT LET the experts run the war. The politicians (Johnson, primarily) insisted on running it themselves. When Nixon turned the actual experts loose, they annihilated the Viet Cong and drove North Viet Nam to signing a peace treaty.
Oh ... and Walter Cronkite was a pathological liar and a communist.
There are experts, and there are people who pretend to be experts. Confusing the two generally leads to bad results.