Katniss' main thing is she's extremely skilled - Fighters aren't. Katniss isn't armoured. Isn't in the military. Isn't trained in any kind of tactics and doesn't have a wide range of weapons. But she's also not some kind of backstabber or Thief. And as you point out, she uses traps a ton, uses natural hazards, and particularly knowledge of nature (which her opponents are shown to lack) to defeat people. She knows and understands terrain and nature - something Rangers did in 5E, but no longer do in 1D&D, I note. Something Rogues and Fighters do not do. She's absolutely what people think of when you say Ranger. Even if you read the 5E description of a Ranger, she's a good match for 6 of 7 paragraphs (a far better match than with Rogue or Fighter, I note), with only the two random and out of place-seeming lines about Rangers knowing magic not fitting.
If we're at the point where we're denying people who obviously fit the pop-culture archetype of a Ranger are Rangers, just because they don't have magic, we can see there's a problem.