It is a fine balance. In rugby league, they train for power as it is short bursts, they can afford the bulk. In rugby union you will see a combination, some of the speediest bastards I have seen play union. In AFL you need mobility, endurance and strength you cannot afford to carry too much bulk beyond the natural size of your frame. In the photo, they are relaxed, they have long lean muscle, good stretching and body weight training will give you that, and it is very deceptive. Callisthenics/gymnastics builds the strongest most functional bodies you will find.