What makes a great fashion photograph? Is it the lighting, the location, the model, the clothes, or post-production? Yes. It's a combination of things that help the photo to have impact.All those things have an effect.
Sometimes the tip of the head, the model's eyes or light in the hair can make or break a picture. When new photographers ask me for advice on how to improve their pictures, I say it's everything. You, as the photographer, are responsible for everything that goes into the frame of the finished photograph.
Lots of people ask about the camera. Yes, it's important. It's a tool. You don't use a screwdriver when you need a hammer. But a good photographer can take a picture with a Nikon, Canon, Sony or any professional camera. Most professional cameras ($2,000+, lenses and accessories are additional costs) are capable of professional images.
Knowing how the camera works in different conditions, the lighting, settings, etc. is a matter of study and experience. That's why many of the top photographers use the same camera for years. To fully know it's capabilities and also it's flaws. Yes, sometimes it's the flaws that make the picture authentic. A little lens flare, the rendering of the background or some softness may add "emotion" to the photo.
Every artist has a "style". Something about how he/she that is unique. It might be to capture real life or maybe to create a wild, stylized image. Maybe it's classic black and white or maybe it's super saturated color.
After working for years, a good photographer/artist has an idea of what they are creating, their style and can then pick the appropriate tools to create the images. That could be old fashioned film cameras, Polaroid images, a fast digital camera to capture action, etc.
New photographers, art directors, etc. sometimes ask why not just use Instagram filters? They are sometimes useful, but certainly not unique. Why hire a photographer to create unique, memorable images and then have them "filtered" to look like everyone else's pictures?