I'm wondering how he comes across as a villain to a Trek novice. I can't watch it without knowing his whole history and feeling the weight behind his words because of that.
I do think Cumberbatch was underused. Rather than have that 9 minute prologue of volcano neutralizing they should have had 9 minutes of Cumberbatch, showing us scenes that made us sympathetic or otherwise. We saw a lot of Khan in Space Seed before there was direct conflict, Khan with his people and interacting with Marla etc.. as a charismatic and mysterious individual. With ST:XII we miss all this, we see him in direct conflict the entire time other than a single exchange with the father. I think he really needed some build up and Cumberbatch being of the caliber he is it's a shame he didn't get it.
It would appear the current thinking is you cannot keep the audience's attention by including those details. Those scenes may have ended up on the cutting room floor.