I do like to watch the size argument threads inevitably deal with on screen issues like this. People argue that TOS-era ships couldn’t be nearly the size of the Enterprise-D while onscreen evidence seems to show the Stargazer and Excelsior class as fairly close. That’s just how special effects were with models and compositing.
As fun as it is to speculate and play around with and as much as we know certain things were designed certain ways, we have to admit that none of this ever really made sense or was all that consistent.
Indeed. I take the official lengths of modern day production more serious: If they say the Discovery is 750,5 m long, then that's the length they have in their computer, that's the scale all hull details are scaled up to, and that's the scale which it exactly has compared to other objects that are on screen.
With
models though the official scale is usually just an approximation. They weren't designed with a specific number in the head - they were designed around their features (some of which are even off-scale towards each other on the same ship - The Enterprise D-s saucer windows are way waaaay taller than the windows on the neck and secondary hull).
Not compared to the rest of the fleet - compared to themselves. If you "fix" say, the shuttlebay or bridge by making the overall ship larger you break scale with airlocks or other features.
Again: We're talking only about up-scaling the original Connie to about 450m (and the Excelsiour proportional). The original Connie doesn't
have that many features giving a scale. Mainly windows - and it has two rows of them on the saucer.
And on the movie refit, ONLY a larger size (~450m) works, even from the outside: If you look at the airlocks (at the bridge dome and the torpedo bay), they aren't designed for a length of 305m - They are designed to fit with
the deck count. And regarding the deck count, the dome clearly is a complete, full deck. And the saucer two decks. And the shuttlebay at least three decks high.
This is
entirely impossible at 305m. Everything would be scaled way too small: Windows at peoples feet, airlocks only big enough to crawl through. The bridge dome only housing the ceiling of the bridge. The "official" size (305m) has
always been wrong. Thus I'm SO happy it was
never, ever actually confirmed in
any canon material on screen.
The original Enterprise has always been around 450m. The Disco-refit only makes that number finally official.