4/5 is as close as would be expected given the size difference. if marquez gives mayweather lots of problems the odds will swing in pacs favor.
You are the one with failed logic The original thread explains perfectly, well perfectly to anybody that can add 2 + 2 together that is, I must make allowances for Americans, isnt betting illegal in America ? {unless you are on Indian land in the middle of the desert or sat on a rock in the middle of a river } Mayweather is 1/5 odds on to beat Marquez , if Mayweather beats Marquez like a 1/5 shot would be expected too, eg by knockout or win every single round, then when Mayweather fights Pacman having destroyed Marquez, he would not go into the Pacman fight as a 'slight' favourite {currently 4/6 on} but a 'stong' favourite {between 1/2 & 1/3}.
Since Pac is the underdogg if this fight goes down, and its the biggest fight of his career, you know he is gonna train probably the hardest he's ever. Come fight night he will be ready.