Why does that argument keep cropping up?
Let's nip this one, nobody in the general audience will "give a shit" about anyone from the Trek mythos beyond whether they provide solid entertainment value. The only people who will care either way are the fans. So it makes no difference whether you use Soran, Khan, Kang, Kor, Koloth, Garth of Izar, or Garry Mitchell. What matters is whether they're well written, well performed, and impress upon the audience a sense of gravitas, pathos, and importance.
Now, i'm not saying Soran was the way to go... I just don't understand the logic behind "the mass audience won't care." They won't care about any of this, one way or the other. They're not in it for that. All they care about is whether the movie is entertaining. Right?