I see your point, and as an animation fan I appreciate these documents greatly, thanks.
I don't know if you've taken the time to actually watch "Victory Through Air Power", but if you do, go to 53:30 and see for yourself: the "Long Range Combat Fighter" depicted in blueprint form (and then extensively in animated form up to 55:23) seems to be a lot more than merely an animator's artistic license. From 55:24 to 54:47, then from 1:02:01 to 1:04:00 approximately, you can see a bomber version that is clearly a lot more realistic than your average cartoon airplane at the time! There is little doubt to me that some Republic staff must have worked closely with Disney people to produce these scenes — as much a tool for war propaganda as a marketing ploy from Republic to sell the government its bomber design, or so it seems! To me it's a clear forerunner of the Rainbow with twin tails instead (kind of a competitor of the unbuilt "Bomber Constellation"), straight from Republic Aviation's drawing boards.
Now back to the aircraft behind Seversky in the photo: true, it doesn't look quite as realistic. And true, it's not featured in this movie. But it shares some similarities with Seversky's transatlantic Clipper design, so I would certainly not discard it as fantasy stuff right away.