For the record, I was the lone "Mario" vote, and not because I believed it was correct.
I've always considered "Jumpman" to be an unimaginative choice, even worse than "guy" (at least Guy is a real name). It's as if they were all sitting around, when someone suddenly said, "Hey! We need a name for the main character." So somebody else spent about 15 seconds scribbling on a napkin, showed it to the rest of the group, and they said, "Yeah, let's go with that. Anything else we need to cover? Ok, another round over here!"