And it also lets Kirk be the one in the big fight with Khan instead of Spock. What is the logic in having the hero of the piece be in a coma during the climactic fight?
Because it simply doesn't work. Even in Space Seed
, Khan should've squished Kirk like a bug.
And if they had went that route, many of the people who dislike the film would've went on and on about how Khan should've squished Kirk like a bug.
Exactly this. Plus, in the new universe the writers have set Spock as an equal protagonist to Kirk, which means he gets his own story thread and character growth. So Kirk and Spock absically switch places from the beginning to the end, where Kirk sacrifices himself, and Spock is doing something reckless.