Easily the biggest flaw in Into Darkness. When I was first watching the film, I expected there would be an ADDITIONAL twist during the Leonard Nimoy scene, with old Spock raising one eyebrow in reaction to seeing an image of Cumberbatch's "Khan", and telling his younger self that the individual they captured is obviously NOT "Khan Noonien Singh". I figured he was just claiming to be the 20th century genetically engineered tyrant for manipulative reasons and we wouldn't learn his TRUE identity until the very end of the film.
Alas, it turned out to be an epic level of lazy writing. Just cast some white British dude as Ricardo Montalbaun's character and the audience will accept it because he's so badass, right? WRONG.
It's even more depressing knowing this was Nimoy's final appearance as Spock. :-(
It could have been easily explained by having them say Admiral Marcus had his appearance (which should be as well known to everyone as Hitler’s is) changed so he wouldn’t be recognized (as a deleted scene or something explained why his daughter had a British accent). But no, even that simple solution was apparently too difficult for them. The “plot” was just a a couple very thin slices of bread to hold the action scenes together. Amazing that people got paid a lot of money to write that.