I disagree with this. Mood is a large part to do with lighting, and finding the right angle of light. Yes it can be enhanced in post, but it is far more impactful to enhance great light than bland light. There’s a big reason landscape photographers like operating at sunrise and sunset. And composition is almost entirely done in camera. All you can really do in post is crop and straighten - which comes at the cost of resolution - and doesn’t help you find a better angle. Not to mention the impact of focal length, f-stop, shutter, etc…
However to me, both are equally important. I see many talented photographers who’s work I don’t wish to look at again due to their processing. Likewise, I see photographers with excellent processing but bland subjects. The best of both worlds is fairly rare - and no doubt many of us would disagree with each other anyway, due to style and taste differences. My favourite images tend to be shot on autochrome, which is kind of at the other end of the spectrum to the high contrast black and white of Matt Black, or the sharp clean colour accurate saturation you see in a lot of digital. Additionally, most portraits you see shot on that medium were taken in nature or at the least older style architecture, with older fashion, which again, is much more to my taste than grey modern cities and modern fashion. So I see subject and style as equally important, but what we each look for in those areas is no doubt different.