I don't know what cards Light converted, but I can't really see any advantage to this over giving Zeru their 30 worst cards and hoping he still wins, unless they couldn't give Zeru a legal deck and leave Majofa with a good vault. Their decks would still have remained hidden, and if they scheduled Majofa's match first, they'd still keep his deck a mystery, and his is the more important battle. (general ups and 1 round ahead) I may be overlooking something, though.