You're assuming that creator intent is an absolute gospel, that what ends up on screen is exactly, 100 percent what the creators wanted.
No, on the contrary I'm very well aware what's happening behind the scenes and I believe I can distinct between "in-universe" and real life. For example: In my current trek tech thread some participants dissect the star map from "Balance of Terror" to prove that the Romulan ship had a faster-than-light drive. Most likely that map was thrown in as a visual effect with little or no consideration whether it actually matched exactly what we saw in this episode.
However, this shouldn't be abused in the general sense "they didn't know what they were doing" as in that same thread I believe I've been able to show that even something as exotic as the power infrastructure of the TOS Enterprise
is remarkably consistent and mostly free of contradictions throughout the first three seasons - coincidental, accidental or deliberate. Seems like they really knew what they were doing, once they decided its dilithium crystals and what these should look like.
There's a saying: "Art is never finished, only abandoned." Few creators are ever perfectly satisfied with the final published or released version of their work. There are always things you wish you could've done better, and as time passes you think of new ideas and go "Oh, I wish I'd done it that way instead," or you notice mistakes that slipped through the editing process, or you just get more skilled with experience and look back with regret on your earlier, less sophisticated work. This is why so many creators go back and revise their earlier work given the opportunity, or retcon or ignore elements of it in later works.
I can't really hear this awful # 1 retcon excuse any more that gave us the special manipulation of Star Wars and a version of Blade Runner that gives me the blues.
True Art like the works of Picasso, Van Gogh or Francis Bacon is "Art" because its raw, spontaneous, straightforward and born in the moment of the mindset the artist was in at the time of the creation. You cannot recreate that spontaneous monent and mindset at a later time. But, again, that's my personal biased opinion. I respect yours and I can only ask you to respect mine.
So while some fans may feel that every last tiny detail in the final work is absolute truth and perfection and must be strictly adhered to -- and that any departure from that attitude is an affront against the work and its creators -- the creators themselves would never feel that way.
First of all, I believe the creators cared about the stories they wanted us to tell and considered "tiny details" secondary or less. However, the "new" Star Trek creators set up new rules and technology (no problem here) but also retroconned these things into past creations (they had never been involved with) which now seemed to contain contradictions and make it look like the (TOS) creators didn't know what they were doing. The simple truth however: The new creators didn't do proper research and that's why the contradictions are there.
Example: In "Balance of Terror" Spock is very specific that he has no clue where the Romulans came from, however "The Savage Curtain" establishes that Vulcan recorded its history at least since the arrival of Surak.
The fact that the Romulans a) come from the outermost part of the galaxy and b) only have impulse drive is a hint that these were Vulcans exiled to the far reaches of the galaxy and left on a planet with no warp drive technology (to ever come back to Vulcan even if they desired). Interestingly the Romans (oh, what a coincidence!) did the same thing with aristocratic noblemen they wanted to get rid of but didn't care to execute.
The "new" creators suddenly claimed that the Romulans were Vulcans that didn't like Surak and left. Hmm...this probably would have been recorded in Vulcan history. And now
it looked like the TOS creators didn't know what they were doing.
Storywise (desire for re-unification) both concepts would have worked, but the TNG one is, apparently, one that is owed to ignorance and...lack of research.