How about the fact that, in the REAL WORLD, aerospace engineers don't build new aircraft out of kitbashes? Things look similar because they are designed for a similar purpose, not because someone literally took parts from another design, slightly tinkered with them and then stuck em on a new design.
What we DO have in aerospace is upgrades (the various knockoffs of the Mig-21 produced by China) upscales (the Mitsubishi F-2, which is pretty much a giant F-16) and modifications (the difference between the Hornet and the Superhornet). You can't estimate the size of any of these aircraft by comparing their parts to similar aircraft, and the same is probably true of starships.