Not to mention this team depended entirely over the landmine strategy in their fight and escape. They lacked any speedy and flashy techniques like William, couldn't show the true might of their weapons as he did.
For all this, the overall strength of the team in such intense and brutal head on battles was quite low actually.
"Hey, we can't keep up like that!" After one hour of doing so, and when the monsters didn't show any sign of slowing down or decreasing in numbers, Sith had to shout at William's growing smaller back, "we will fall down soon on this rate!"
"Just keep following me!" William knew from the start the crucial dead weak spot of this team. And so, he never planned on just running around aimlessly like Sith and others thought wrongly.
He just used the sea of monsters here to shield them from the many clones of the Nightmare monster. And his little plan succeeded.