Just my two bits...
It's true that most of the terrain in RTW is "average," however I have had battles similar to MaximusDecimus's except where occasionally MY forces have been practically atop a huge hill (or small mountain, depending whether the glass is half full or half empty, LOL).
However, I do agree that trees and the like seem to offer no real advantages/disadvantages other than to block the view of the camera! You have a valid point.
"He said, 'Why should I tarry?' And smiled with tranquil eye; 'In destinies sad or merry, True men can but try.'" Sir Gawain and the Green Knight (Lines 562-565)