If you are writing a serious detective work, making sure you get it as real as possible, while still being entertaining, then the detectives are going to be genre blind, otherwise the cops will arrest someone who says something inconsequential at the start of the investigation.
In a 5 vs 1 situation, the 1 tends to get his head kicked in.
For the first example, they won't arrest someone just for an inconsequential remark, but they might take note of that remark as potentially important. There's a degree of overlap between being Genre Savvy
according to the rules of fiction, and being clever and observant according to real-life standards.
For the second example, I think it's a little silly for the hero to think he can win a fair fight against five people just because he's the hero, but it's even more silly for the hero to actually win. Much more interesting, at least to me, is either a character who fights out of desperation and gets his ass kicked, or a character who knows full well he can't win fairly (either seeking to win unfairly
, or just running for dear life.)