This concept of "high ground" hasn't been an issue in any previous battle ... it was merely a convenient and highly lame way to end this fight. And yeah ... had Ben exploited a weakness in Vader that was rooted in Anakin's fall to the dark side (re: attacking Dooku in a fit of anger and losing his hand) it would be far more acceptable than nonsense about high ground.
And the attempts at explaining away the construction of the Death star don't work for me AT ALL. Sorry, but it just doesn't add up. Twenty years to construct one Death Star ... and six months to two years to construct a second? Not even Henry Ford could achieve that feat. Lucas was feebly trying to tie-in images from the original film to justify Revenge of the Sith in the face of all logic.
It seems to me that you're choosing to file plot holes YOU don't want to acknowledge as "nitpicks."