Quote - "the ...Falcon was the only ship built  to life size proportions"..

Actually, only the left half of the Falcon was built life-size (the side with the cockpit and ramp). The other half was created with the use of matte paintings.
 
Since they didn't think Star Wars would be popular, they destroyed the exterior Falcon sets after filming was finished... and had to re-create it for Empire Strikes Back. This time, the entire ship was built (especially for the scenes on Hoth where Han and Chewbacca walk on the exterior).
And, no, the exterior ramp did not actually lead into an interior set: the actors ran up the ramp and hit a wall. But, with clever editting, it looks like the actors ran up the ramp, through the interior, and into the cockpit.
 
The star destroyer in Star Wars seemed so big because it was the first time spaceships had been filmed like that: the slow movement made it seem like the ship just kept going on and on and on.
Even though the Enterprise, the Death Star, and 2001's Discovery may be the same size or larger, those ships were never filmed like the star destroyer.
 
--John

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