Sergio is a counter puncher with huge power. Sergio is much bigger. Sergio dances around him, and KOs him with a counter shot in the middle rounds. If Ishida can do that to Kirkland, imagine Martinez. Of course he has a punchers chance, but a smart counter puncher like Martinez won't be enticed to brawl.
Took the words out of my keyboard. Most importantly, Sergio has the better experience in both age and activity.