You’re missing out on one significant component as to why ACG’s book was the first to kick off precode horror- it was the first horror series that came out regularly. AITU #1 was not a one shot as we know. It was a successful and continuous run that had a following given ACG kept the run going, and it went on to be one of the longest running horror runs in comic book history. Gaines and company were already doing crime in 1949 and things moved at a slower pace during that time. Had AITU not succeeded, we may have never seen EC Comics take on horror the way it did (Moon Girl #5 did have EC’s first horror story but nothing followed and that may also have to do with the fact that it hit the newsstands at around the same time as AITU #1 during the Fall of 1948 - before ACG’s intent on making AITU a continuous run) but rather stick to crime, romance, westerns, and war. Thankfully, ACG succeeded and EC went much further and took horror to its greatest level, which is one of the main reasons why the 1950s comics are not Golden Age Comic Books. As for Eerie Comics, it was not the first horror comic. Gilberton’s Classic Comics title produced the first horror comics that were adaptations of classic horror stories like Dr. Jekyll and Mr. Hyde. Eerie Comics #1 was the first horror comic to have original material and that’s what makes it a special book.
CDNP #22 is the first comic book entirely dedicated to crime that also started the crime genre, which later saw the romance (with Young Romance #1) and horror (AITU #1) genres that went on after the superhero genre ended with Second World War and postwar era. Fascinating time for the history of the American Comic Book!