The roots got denser and more fierce with their attacks as Arnold and company were nearing the 'heart' of the tree. However, Arnold was the sole target of the roots as he was the only one having a life force there as the rest of his summons were either already dead or made of metal. This made it easier for his summons to wreak havoc on the root suing their new gear.
As for Arnold, well he was having a fun time dodging and attacking the roots at the same time. He was being forced to always be on his toes. He had to be observant and cautious to not get entangled between the roots or else it might as well be over for him.
