HMMMMMMMMM..............just photoshopping for fun. What if the character of Lt Cdr Gary Mitchell had not been killed of and remained the old friend of Kirk, as well as the second officer? How would TOS have played out?
Some people think Mitchell was the first officer during "Where No Man...", so Spock would've been second officer.
If Mitchell were retained, then he probably would've brought the emotional component to the triumvirate that McCoy did. So what then of McCoy?
Then there would be no McCoy as we know him. The doctor would be a secondary character at the level of the other secondary characters.