As for the second reason why Xie Feng decided to climb the giant Abyssal Dragon's body to the top instead of just climbing a part of it, it was because he wanted to make use of Ling Long's attacks in the best possible way.
By attacking where the scales had been broken by Ling Long's powerful fists, Xie Feng's attacks could practically ignore all the defense of the Abyssal Dragon that had been weakened by Shen Xinya's destiny skills. Moreover, if he attacked the head, the damage could be increased by another notch unlike if he attacked a foot or a claw; after all, the head was the weak point of any creature and the damage received in that area was a lot more dangerous.
Although Samsara Online was a virtual world that was governed by stats, simple and basic things like this were no different from the real world.