I solidly agree, there are no more signifcant commercial aircraft than the DC-3. Some rival it in terms of era/signicant performance and construction advancements, but the Doug is among the top of the field that resulted in MAJOR aviation improvements.
Another that I consider significant but not well recognized, the Boeing 247. Huge structural advancements and significant performance increase, but a little late and found itself pitted against the DC-3. Understandably it was not heavily produced, but a really good airplane it was.
I had the opportunity to see the 247 at the Seattle Museum of Flight, while it was undergoing some restoration work. Partially dis-assembled it was clear that the structure was really stout, very robust and strong. Just too small and couldn't compete adequately, when going up against the -3.
Probably not sufficient interest among modelers to warrant producing a quality 247 model, but I'd sure like to have a few.
Patrick