Are there any historical examples where the Lightweight won? The only one I can think of is Armstrong beating Ross.
With the two divisions usually having talent in them, there are a lot of potential match ups. You'd figure the lightweight is up against the odds.
Were those the weights? Armstrong was below light weight, Ross near Welter. Close enough Light weight beats the Welter.
I don't think Armstrong ever defended his FW crown. He moved up and was fighting in the 130's lbs on a monthly basis, before going after Barney Ross's WW crown. "Later in 1938, Armstrong, still the Featherweight division world champion, challenged a fellow member of the three division champions' club, Barney Ross, then World Welterweight Champion, for the title. Armstrong, at 133½ pounds, beat Ross, 142 pounds, by unanimous decision, adding the World Welterweight Championship to his belt. He then lost weight and beat World Lightweight Champion Lou Ambers by split decision, becoming the first boxer ever to hold world championships in three different weight divisions at the same time. He decided not to make the 126 pound weight anymore and left the featherweight crown vacant."
The great KID LaVigne fought and beat Walcott twice. One of the greatest books you could ever read is "Muscles & Mayhem; The Saginaw Kid and the Fistic World of the 1890s".. Simply great.