As I reflect on the film, I think that having Chekov sub for Scotty actually highlighted a problem with his character in the ensemble...we don't really need two characters to provide manic physical comedy relief. They need to find a new angle for Chekov.
The Old Mixer wrote:
it's a pretty common conceit in these types of series that you never use a nameless extra to do a job that one of your established characters can do.
Which makes sense narratively, but clashes with reality, where the exact opposite
is the norm.
You want reality, you might be watching the wrong movies....
Even nuBSG, with its grittier and more naturalistic approach, couldn't escape the inconvenient dictates of drama...hence the "SuperStarbuck" phenomenon.