Discovery's look isn't just unique, it's the first in Trek to be directly contradictory to what's previously established. That they acknowledge they had to change the classic Enterprise to fit their version of the world spells out clearly that the world's are not the same.Not sure where you're getting this from, apart from perhaps overselling the phrase "Discovery's world" or "our world" used in panels. The same phrase pops up in the DS9 Companion, "the world of deep space nine". It's just shorthand for the show's look, feel, characters, themes, etc. Each of the Trek shows had their own 'world' in that sense. As far as I'm aware there's no official source contradicting the assertion they see this show as Prime Timeline.
Obviously however, the Discoprise won't be the "true size" of the TOS Enterprise. It'll be it's own intended scale, which they think looks best next to NCC-1031. They also altered the proportions significantly.The answer to this is actually super easy:
Encyclopedias are non-canon.
The "size" of the TOS Enterprise was never mentioned on screen.
What DO we have - deckplans, two visible levels on the saucer - fits much better, if not ONLY with an upscaled TOS Enterprise (like by a third bigger).
Thus: The TOS Enterprise officially "IS" bigger. This is not even a retcon (because, again, every mention of her size was NON-canon to begin with). The bigger size just IS the true size of the TOS Enterprise, and all previous encyclopedias have been wrong about it. Period. Much like they have been wrong about what was the first human Warp ship and early humen spaceflight history before.
Even if you follow CBS' doublethink and play along that nothing's changed in Trek, if someone asks what the Enterprise looked like in the Pike era of the Prime Universe, that you'd have to give two answers shows they're not really the same world.