King Daniel Into Darkness wrote:
But Chekov covered for Spock in TOS, despite not being part of the science divison. What were Spock's blueshirts doing then? Or in TAS when Arex covered when Spock was away?
...or even TNG, when helmsman LaForge was suddenly the best man to take over engineering in season two? Were Argyle's people really that useless?
As usual, you hit the nail right on the head.
From a narrative point of view, having Chekov in Engineering makes sense. It gives him a bigger role and focus and showcases more of his skills. Having a one-off role for the position of Chief Engineer is a mistake as the character will be quickly cast aside. Unless Scotty is replaced permanently, it only makes sense to have a main cast member fill in.
Scotty himself was assigned to the Enterprise over any one of the possible replacements for Olson. I wonder why Spock didn't assign someone as chief engineer immediately after the Vulcan incident?
Besides, I wonder how helmsmen McKenna and Lieutenant Hawkins felt in Star Trek 2009 when they were permanently replaced on the Enterprise by Sulu and Uhura, respectively?