Joe Louis was possibly an underdog against Primo Carnera because of the size disadvantage. He might have been an underdog in the second Schmeling fight because he got knocked out in the first one. He was also so old when he fought Marciano he probably wasn't favored. Chocolatito was an underdog against Yaegashi who was the recognized man in his division. Chris John was an underdog against Juan Manuel Marquez. Sonny Liston was probably an underdog going against the younger and taller Chuck Wepner. Valero didn't have a long enough career.
Every fighter has been an underdog at some point in their career it’s part of your progression when you step up and challenge yourself, you have to take on opponents with more experience with higher ranking and better resumes, meaning that you will have to be considered an underdog at some point. So yes they have all been underdogs at some point. You could even argue that you will always be an underdog in the eyes of someone, no matter how far you go in any sport you will never be in a position where every person will hold the opinion that you are the better fighter.
