Floyd Mayweather is a boxing prodigy. Like Mozart, he was born with tremendous natural gifts. But also like Mozart, Mayweather was set to work developing the skills necessary to use those gifts at a tender young age.
Boxing is an art. To reach the elite level, a fighter needs rare physical talent. But that natural talent will amount to little if he doesn't develop his technical skill.
Note that this ranking is not a pound-for-pound ranking. But it does fairly closely resemble one. More often than not, the best fighters in the world are the ones who have the most well-developed technique.