Why does it have to assume that? Where does Intelligent Design preclude Evolution as being mutally exclusive in its theory?
Please, show me how you drew such a conclusion.
I know of no ID-ers who accept evolution above the micro level. You're welcome to put yourself in this position, but you're the first in my experience if you do. If you don't shoot down evolution, you simply don't need the Designer.
ID-ers spend so much time trying to shoot down evolution that there's essentially no other intellectual content to their literature.