Pete's a considerably better athlete, but Roger is a more skilled tennis player.
Roger is a very good athlete, who happened to have found the sport that best suits his particular set of talents most comfortably.
Sampras was a superb athlete who could have used his athleticism to get to a high level in many sports. Tennis at the time was best suited for him, these days the game has probably become too dependent on more continuous stamina output for it to be his best fit, though he'd still be very good.
It's easy to see Sampras wrestling freestyle in the Olympics or playing judo, playing in the backfield in American football, sprinting down the track or hurdling, chasing down a fly ball in baseball or cricket, even crossing someone up and dishing out a pass on the basketball court or hanging from the rings in gymnastics.
For Federer, other than maybe figure skating or football, he just seems grooved perfectly in his frame and athletic gifts to be a tennis player, but not those other things.