The fact that even a Taoist Monarch could fall indicates that this great battle is far more terrifying than they had imagined.
Even though both of them are at the True Immortal Sixth Layer Heaven, just one step away from becoming Taoist Monarchs, they also understand how powerful a Taoist Monarch truly is.
Initially, they thought this battle, despite being a contest among Taoist Monarchs where they might personally take action, would be limited, with mutual restraint, since even if a Taoist Monarch lost, they would still retain a fundamental base of interests. Thus, the real fierce battles would involve those below the True Immortal Sixth Layer Heaven.
Given their strength, as long as they don't face a powerful Taoist Monarch directly, it's not particularly difficult to save their lives against any True Immortal or God, even if they're at a disadvantage.