That it is science fiction doesn't mean that basic motivations and logic can be ignored or that important plot points introduced in the previous part of the same two-parter can be ignored.
Yeah. To me, there is a big difference in filling in blanks (Where is Chekov in season one?) and making excuses for bad writing.
I’m not that much into the head canon stuff, anyway. Either it’s on screen and it makes sense or it doesn’t.