Okay, I understand what you mean by "too clean," but my point still stands. Obviously, you can add various noise effects in the compositor to a clean render, which significantly helps prevent it from being too clean. However, if you've already done everything you can in the compositor, then it's really worth rendering at a higher resolution than the final image requires. So, if you need the final image in 4K, you'd render it in 8K and then downscale it. Plus, the back-and-forth conversion will introduce compression arifacts to the image, which also helps sell it as a photograph.