On a Monday night in Las Vegas, Ryan Garcia reminded the sport of boxing that proximity to greatness is not the same as readiness for it. The American champion stopped British challenger Conor Benn in the second round, retaining his WBC welterweight title in a contest that revealed, with quiet efficiency, the vast distance between two men at different stages of their becoming. Garcia, composed and precise where Benn was eager and exposed, delivered not so much a fight as a verdict — one the sport had largely anticipated before a single punch was thrown.