The two Druids were well aware of Li Yao's attack power, so they opted for a survival strategy from the start, convinced they had no chance of killing him, but at the same time, they didn't believe Li Yao could instantly annihilate them.
They thought they had a very reasonable understanding of their own abilities, and it was clear that their plan was simply to protect themselves and then rely on the Dragon Clan to kill Li Yao, thwarting Starfire from taking on this task.
They also came from major guilds, and although they were competitors just moments ago, Li Yao's arrival changed the dynamic of the situation.
This shift caused them to unanimously ally against an external party without any discussion, and that external party was naturally Li Yao.
Moreover, they were members of the Anti-Star Alliance, and were naturally enthusiastic about disrupting Starfire's progress.