so basically the story of Kirk's five-year mission is still the same just the way we saw (Technology wise) is up to interpretation?
All fiction is mutable. It is subject to change by the authors/ right holders, as well as audience interpretation of the events presented. It is hard and fast as fact until the next iteration comes along and adjusts it. Which is exactly what TMP did to TOS. So, yes, TOS is, and always has been, open to interpretation.
TAS did it before that. And TOS did it before that. (e.g., "The Cloud Minders" vs "Amok Time": "It is a thing no out-worlder may know [etc]".)
Actually the full line is: " it is the thing no outworlder may know... except those few who have been involved..."
That would be the etc part that I wrote. The million credit question is, how was Droxine involved? Spoiler As far as Spock was concerned, she wasn't.
Flirtatious Kirk voice: How does Droxine want to be involved? (Sorry for the non-sequitur, the question gave me a flashback to Mirror-Marlena.)
This will be the key retcon. If he's already a Vulcan physiology expert, it's a no go, but if he's not yet THAT, and takes the leave to go to Vulcan and then Piper takes over... and then McCoy comes over with Kirk -- that'd make sense.
"Through both seasons, Star Trek: The Animated Series faced the reverse situation of The Original Series with regard to its popularity: ratings were high, but skewed away from the young children which Saturday morning advertisers were trying to reach, being more popular with adults and older children..." [Mangels, Andy (Summer 2018). "Star Trek: The Animated Series". RetroFan. United States: TwoMorrows Publishing (1): 25–37.]
The only problem with that is why he's not treating Sarek in Journey to Babel - you'd think an expert on Vulcans would be useful. Perhaps we only saw McCoy's shift.
But this is the 23rd century, so people could look younger while being actually older (they did it with Picard/Stewart). Heck, when I think about my childhood septuagenarians back then looked a lot older than they do nowadays.
I'll only be slightly irritated if they retcon some stuff. I've never been a stickler for the minute details like the timeline of the Chief Medical Officers of the Enterprise. It just bothers me that most Trek fans know their canon backwards and forwards and would know stuff like this. Like heck, hire the Okuda's or the Reeves-Stevens' to be your timeline keeper. But at the end of day, if the stories are good, I can handle a little mudding of the timeline.