I didn't want to take my silence to your last reply to my post as acceptance of your points because I didn't agree with many of your conclusions.
First off I want to tell you that it was not my intention to imply you were being dishonest with me. I didn't care for your 'dismissal' but I can understand if you think I was implying deceit on your part. What I did feel then, and still do, is that you were sidestepping the question about Uhura being defined by Spock.
I can agree that she has seemed to taken McCoy's spot as the third pillar but I would argue that it is an issue of style and image more than substance. McCoy played a key role in helping frame the intellectual and/or moral issues affecting the crew, vis a vis his debates with Spock and his advice with Kirk. NuUhura, while starting out as a gadfly of Kirk's during the Academy scenes, has now been relegated to having her conversations with Kirk revolve around her relationship with Spock. She provides no opposition or different point of view. She added nothing to the political discussion in Into Darkness. Unless it's about Spock and how he feels about her, them, or himself, she doesn't have much to add at all. Her character is very limited. I'm not saying that isn't a step up from what Nichelle Nichols had to work with, but I'm not singing hosannas about it either.
Granted Zoe probably is the biggest star of that cast but that doesn't automatically equate to them finding something to do with her if her relationship with Spock ended. With TNG, LeVar Burton was the best known actor to US audiences at the start of the show but that billing wasn't commensurate with the development and screen time his character got. So it remains to be seen if they do break up Spock and Uhura and what would happen to Uhura afterwards. As it stands for me, Zoe being a black Latina and a woman helps sell this new version of Trek as something different and her relationship with Spock also does that, but underneath it is still largely a story dominated by white males, as was the case with Into Darkness (Kirk, Spock-white Vulcan male, nuKhan, and Marcus). Zoe is not quite very pretty brown wall paper, like Halle was in the X-Men films, but she isn't that far removed from it. Better than Nichelle's Uhura-let me repeat-but the level of empowerment is going to continue to be a subject of debate.
While you are right that both actors were of European ancestry (which is a real world thing; and why do you get to use the real world and I don't?
), Khan Noonien Singh, as envisioned by Gene Roddenberry was likely not. As you pointed out, they even darkened Montalban's skin in "Space Seed" to highlight that he wasn't a white guy. And if we are to believe that the alternate universe timeline was largely unaffected until Nero's incursion Khan should still look like the Khan of "Space Seed". Even the fairer skinned Khan of TWOK had more tint to his skin than Cumberbatch's did. I'm guessing-hoping-that the upcoming Harrison comic book will explain he was surgically altered, which would make sense within the context of this story, though I wish they had just cast an actor of color.
Regarding Into Darkness I don't know how exhausting the casting search was. I only read about Del Toro, which I said was a good thing previously. I don't know if they did even look at South Asian actors. It would've been great if they had even corrected Roddenberry's faux pas with Khan initially, but they didn't. They took a character of color and hired a white guy to play him. That's whitewashing.
I disagree with your description that 'plenty' of films have gone the route of casting blacks or other nonwhites into 'white' roles. I don't think there is an equivalence between whitewashing and nonwhites being cast in some white roles, and especially when you factor in the entire history of Hollywood.
There have been some and some very prominent casting choices. Part of the reason for that I feel is a continuing lack of support for films with nonwhite subject matter or films centering on specifically nonwhite characters. Further I think the idea of whites as default human beings have in a way made many white characters indistinct enough to be played by anyone. There remain a dearth of roles for people of color and characters of color so when one as iconic as Khan goes to a white guy that's one less opportunity gone and that affects both actors and fans.
For some of your examples, Samuel L. Jackson played the Ultimate Nick Fury. While regular Marvel Universe Nick Fury is white, the re-imagined Ultimate Fury was based on Samuel L. Jackson. So he's playing a character that is based on him.
Regarding Kristin Kreuk as Lana. Kreuk is half-white and I wouldn't have known she was half-Asian unless someone told me. She could easily pass for white so I don't think that's as much of an issue here. Sam Jones as Pete Ross would be a better example for Smallville. Though I do think it's good that her Asian heritage is being acknowledged.