The answer is yes, reducing time and making the game more dynamic adds to the complexity. But that is not the only difference between football and soccer that affects the complexity. One sport is played with hands, while the other is played with feet and other body parts. The variety in skills needed is greater in soccer. Everyone is "QB" and everyone is a "receiver" at any given time. The movement and positioning of the players is continuously adjusted. In soccer, all players participate constantly in attack and defense, as well as in transition phase from one to the other, often on the fly. All those things add to the complexity.