The thing about 4k is it exacerbates the CGI lighting issues because there's so many more pixels to calculate. The sun is NOT a single point light source. It has a visible disk. And ambient light does NOT emanate evenly from EVERY direction. Most of it comes from the sky dome. Both of these make it very expensive to calculate realistic lighting, reflections, and shadows at high resolution.
The thing about 4k is it exacerbates the CGI lighting issues because there's so many more pixels to calculate. The sun is NOT a single point light source. It has a visible disk. And ambient light does NOT emanate evenly from EVERY direction. Most of it comes from the sky dome. Both of these make it very expensive to calculate realistic lighting, reflections, and shadows at high resolution.
Watch the water.