Crysis 1 Retexturing Project replaces the Original Textures with Hi Res Textures. (Textures from Texturelib.com, Freepbr.com, Texturehaven, CC0 Textures)
So the Clouds also can be changed on skyhdr Shader, so in the End you have great Sunlight and individual Clouds. But also the Clouds need lot of Attention to look natural. So the Clouds on skyhdr are moving Clouds and not static Clouds like in static Skyboxes.