Rios would have beaten the ever living shit outta Katsidis. People tend to forget that Brandon was actually a good fighter at 135 circa 2010 when he stopped Acosta. He remained a good fighter up until the first Alvarado fight. His career fell off a cliff after that. Katsidis was nothing more than a fringe contender. It'd be a fun fight, but Rios would have grinded Katsidis down and knocked him out late. A much better match-up would be prime Rios vs Isaac Cruz.
