You obviously don't, nor ever have, played tennis seriously at a high level. To think that a tennis player, who needs to play for several hours on end 11 months of the year, needs legs like a rugby player is ridiculous. Every kilo over what you need is more strain on the knees, ankles and feet. And not to mention every extra kilo you have to lug around the court. Even if a player did decide to train heavy legs all year round, which is ridiculous, you do realise they wouldn't gain much, if any, weight at all given they are running 3-4 hours today around the court? In college i would drop 6-8 pounds in 3 months of play in season after the off season. PLaying tennis strips your body of everything you don't need. Tennis players probably focus more on the athletic side of the sport now than ever before, and i can only think of cycling and boxing as sports with more finely tuned bodies. Novak and Federer are perfect tennis specimens. Strong legs with very lean upper bodies who generate power from timing, legs, and core. They would have extremely strong forearms and wrists by the way. Whipping a 350gram wand around several thousand times a day will do that. Again, it is highly specialised.
Those bands that rafa is 'messing around with' are training the little muscles in his back (rotator cuff) and legs used for stability and injury prevention. A tennis player these days is extremely fine tuned, strong core and legs with a very lean physique is required so that you can move and play for 4-5 hours on end. SUre carter is very explosive but he is a freaking rugby union player, the least aerobic form of rugby around. Of the 80 minutes they play he probably only actually runs 40 or so given scrums, line outs and stoppages. And he plays once a week. He has to be much stronger than a tennis player cuz bloody back rowers at 115kg try and break him and he has to be able to break a line of men all over 100kg. Carter is finely tuned for his sport the same way rafa is. And by the way, no way is carter over 105kg, id say he would be more around 95-98 maybe.