I think the only thing you might be missing imo is that Violent Night matches what most people expect and probably want from a violent Santa movie. I also enjoyed Fat Man a lot more than Violent Night, but FM is a lot dryer of a movie than VN. For me, the comedy came from its concept and execution as opposed to lines in the script. Meanwhile VN featured jokes and action in almost every scene.

Plus everyone loves David Harbour and Mel Gibson will always carry his baggage