Who is the more domineering one?

The name of Pei Qing's junior brother is Jing Yunhe. He had outstanding talent and was a heaven chosen immortal king character. He spent roughly over 90 years at the immortal king realm and his foundation had already been stabilized. His combat prowess was also undoubtedly extremely strong.

As for Qin Wentian, he just entered the immortal king realm and his cultivation base wasn't steady yet. Most probably, his law domain was only that of a single law-attribute. Such a combat would be of no suspense. Hence, Pei Qing asked his junior brother to deal with Qin Wentian. Although he felt that he already overestimated Qin Wentian by asking his junior brother for help, it was clear that Pei Qing's objective wasn't as simple as merely defeating Qin Wentian.

Before this, Jing Yunhe had already received a voice transmission telling him to act with no mercy, to slaughter his opponent.