Open the Atmosphere Box. The reason the sun still looks so bright is all the atmosphere between the camera and the sun, filtering and scattering the light. To correct this, drop all the Half-heights and Densities to start with. Personal preference can have a lot of influence here. Play with the setting to find what you really want, because technically, we've already created bliss. Here for mine, I lowered the Half-heights, and Simple Haze Density and raised the Atmospheric Blue and the Light Decay.