Re: the issue of Kirk taking the promotion, IIRC the original 'Phase II' version of the script took a slightly different tack: everybody onboard the Enterprise could see that he made the wrong decision in accepting the promotion except
for Kirk himself. It's only when he's back in the center chair (at Admiral Nogura's insistence) that Kirk finally remembers his true calling, to command a starship.
Recalling from memory: there's an early scene in that first draft script where Kirk meets McCoy again on Earth (now a freelance physician), before
his meeting with Nogura, and Bones urges Kirk towards starship command again. Then in the meeting about the threat, Nogura himself has to damn near order
Kirk to take personal command of the Enterprise again, as Kirk keeps recommending other options except the 'obvious' one. But once he's there, Kirk begins to remember what he loved about starship duty, and only then
does he realize everybody was right but him, and that accepting the promotion was a mistake.
The final version as seen in TMP is in some ways more dramatically pleasing, but it does rather show Kirk to be somewhat ruthlessly pursuing starship command again at the expense of other officers. Notable is that McCoy's perspective does a complete flip from what it was in the early draft: instead of urging Kirk to go back to what he was best at, he instead recognizes Kirk's "true" reason for taking Enterprise back from Decker, and admonishes him accordingly.