James Toney didn't teach himself...He was taught by Bill Miller, one of the greatest trainers ever, himself a student of, I believe, Whitey Bimstein. Bill Miller also trained Emmanuel Steward when he fought as an amateur and was the man behind the scenes in much of the early Kronk success.
Bill Miller was a huge fan of Ezzard Charles and his style of fighting, as is anybody that knows boxing. And a guy being as relaxed in the ring as Toney, that comes from having a teacher that preaches that to you from the first day in the gym. "Relax. Stay loose." Over and over again.
There aren't very many guys that can translate 'only' being naturally gifted athletically into an extended period of success in boxing...Being able to run fast or jump high or however you quantify being athletically gifted hasn't much to do with fighting, if you're fighting guys that know about fighting.
On the other hand, while Toney and Hopkins and Marquez may be 'students of the game' it is not reasonable to suggest that they are not physically gifted as well. They just chose to specialize and focus those gifts, rather than to brag about their basketball abilities.