AFAIK, that’s actually a myth. The people doing the “experiments” in the concentration camps were not the best and brightest in the first place, and their methology and note-taking was far from rigorous (since a lot of the time they were actually trying to prove their favorite racist nonsense theories).
WWII did spur huge advances in medical knowledge, but almost all of it comes from regular military hospitals (mostly on the Allied side, but occasionally in Germany) treating various wartime injuries and working on recovery and recuperation. IIRC, there was a Soviet neurologist who pushed the state of art of brain surgery and general understanding of the human brains, simply because over the six years of war, he was supplied with more cases, with more varied brain injuries, than he might have seen in an entire peace-time career.
