Simply put, Tokugawa can't solo constantly without letting Kadowaki touch the ball at some point.
Let's put it this way, Kadowaki has no hope of returning Inui's Waterfall.
As long as Ohmagari/Inui serve at Kadowaki, then its over. In Volleyball if you aim your serve at a player that is total trash, you kinda have the key to victory.
Unless Tokugawa can tell the prideful Kadowaki to step off the court and let him solo things then he can't.
And the way Volleyball is set up, Tokugawa can't hit winning smashes non-stop. Winning smashes almost always require someone to "receive the shot", then set up the person who is going in for a Spike.(Volleyball smash).
So basically, Kadowaki single-handedly loses this for his team.