I thought Commander John Harrison was more interesting than whitewashed Khan.
Agree. All that would be needed is for a tweak to the 'people in the torpedoes' plot point, and Khan could be effectively written out of the movie.
They could have kept him as John Harrison, maybe reveal that he was one of Khan's followers instead and rather than 72 people in torpedoes it could have been 3 or 4 out of many and instead of his "people" inside (who we never meet) it could have been his wife and children. It would have upped the stakes for Harrison, create more empathy from the audience and make Marcus look like that much more of a dickbag. It would have been a slight nod
to TWOK by making Harrison simply a disciple of Khan rather than the headbutting we got instead.
Don't get me wrong, I enjoyed the movie, I simply think it could have been better had the writers been a bit more creative.