I can point out the flaw in your logic. You wrote: "I thought the "I acted under orders" was not a defense against war crimes." You are correct that "acting under orders" is not a defense in a criminal war crimes trial. But (1) there was no "defense" here at all because there was no trial. The court ruled (correctly) that there was immunity from the suit itself - U.S. district courts in Manhattan don't entertain lawsuits against foreign government activities. Nor should they. And (2) this was not a criminal case at all either. It was a lawsuit for money damages brought by a private citizen and activist groups. So, essentially, contrary to what you wrote, this ruling has nothing to do with Nazi leaders' criminal culpability.
from the article: U.S. District Court in Manhattan clears Dichter in war crimes suit