Batman was not the second DC superhero (after Superman) or the first non-powered superhero or the first masked superhero or even the first non-powered masked comic book superhero. A character named the Crimson Avenger was all of those things before him.
Precursors from other media included the Scarlet Pimpernel, Zorro, the Shadow, and the Phantom. They also lacked powers, wore masks, or both. Yet today, none of these characters (some of whom Batman was in part based on) are as popular as Batman.
I believe this is in large part due to the wrenching origin Bill Finger gave the character, but also because of the skillful way in which Bill blended various elements from other characters. Though those characters were familiar to many at the time, Batman still seemed fresh. It was as if Batman were a recipe in which even a pinch more salt or a teaspoon less of vanilla could have altered (and maybe ruined) the result.