Sun Xingbiao's words hit the nail on the head for both the Crown Prince and Chen Wenbo. If they had known how powerful Qi Tian was from the beginning, they would not have chosen to treat the Imperial Master Mansion and Qi Tian like pushovers. Or they might have employed Gold Core cultivators of the second or third level at any cost to assassinate Qi Tian, thereby avoiding the current troubles.
However, all these second-guessing actions are just after the fact. If given the choice again, they would probably still opt for the initial plan.