You are correct to understand that Graphisoft's implementation of the wonderful LightWorks product is deficient. But there have been some improvements to the Sun shader since Archicad 9 that preclude using a sun object. You can now ask the Sun Shader to create a "Realistic Sun" that makes more diffuse shadow edges.
Softness and realism can be improved by adding color to the sky object and the sun shader.
Certain LightWorks conditions slow rendering down:
1: refraction in glass
2: "Best" Antialiasing
3: "Best" Method
Get my book.
For faster tests, you should create a view that shows principal elements to render only essentials.
As for critiquing your rendering:
1: move back and tighten up the view. This is an overbearing and scary wide angle shot.
2: Use a lower sun angle to illuminate the overhung areas.
3: Eliminate evidence of repeating surface patterns. [driveway[
4: darken the lawn.
5: make glass less shiny.
6: add roughness to the plain areas - these are stucco?
7: too many materials in the project - chaos to the eye.
8: background sky image is a problem since it is a telephoto shot with a wide angle view.
Dwight Atkinson