Valuev's tricky. I don't know if I'd consider him because I believe being born with that size with the ability to have the stamina he does is a pretty significant gift. If you interpret gifted as just being a natural fighter, a case could be made for him- he's definitely a guy who had to work hard for his progress.
Unless you consider his physical advantages as gifts. The guy basicaly had size, fair speed and the rest was sound fundamentals.
how about sven ottke? i saw some of his fights i dident even know how he was effective but he was and became if not a near great then a very good fighter with primarily intellegence.