The extra thickness of the fillet also provides strength, and its smooth contour distributes stresses evenly.
(For additional strength Schwinn also brazed steel sleeves into the interior of its frame tubes at the joints.) Fillet-brazed bicycle frames are strong and have a neat and clean appearance, but they are uncommon because of the additional craftsmanship required.
When I've had my hands on the actual pieces of metal, and then taken the time to actually look, and measure, and look again…I've learned a few things! Color choices very definitely were changed from what is listed in the consumer catalogs. It was common for color choices to be different from what was listed in the catalog. There were definitely whole bicycles available but not listed in catalogs, and also listed bicycles not actually available!
And some of the “experts” know the real facts so much better than other “experts”! Less common were equipment changes, but those happened too! And Schwinn catalogs were much better than most catalogs!!!
Then all of the details have only one remaining question: is that component part original, or a replacement?