You have to wonder how he got the nickname, though, given all the other Nazi shitheads who came up with the idea of searching crawlspaces. It wasn't like this was a foolproof trick that only Landa could have seen though. But after that nickname is established, Landa spends the rest of the movie showing how undeserving he is of it. When the sole survivor of the prologue, Shoshana, later eats with Landa, we hope that he won't pick up on her fear and hatred of this monster who killed her family. But flip that around, and you've got a supposedly brilliant detective who doesn't recognize that the woman he's eating with is unusually terrified of him.
It's not like he has any reason to pretend he doesn't recognize her. A big movie premiere which Hitler himself is attending is planned for the theater she runs, and he's supposed to vet her for security purposes. Yet he fails to pick up anything amiss. (Note: She is plotting to fry the theater with all the Nazis in it, which we're pretty sure counts as "amiss.")
Later, when it comes to foiling the Basterds, Landa just gets lucky. As in, he finds a napkin with the name, autograph, and fresh lipstick of the Basterds' mole at a crime scene with three dead Basterds. They may as well have thrown in her dental records and a signed confession. Then, even with all of those advantages, Landa needed to coincidentally be fluent in Italian to be able to spot the disguised Basterds when they pretend to be Italian. That's not genius detective work; that's applying your experience from a year abroad.