Monitoring the sacred sect was not something that could be done in a day or two. The sacred sect might not be ready yet. Otherwise, they would not have only occupied mang mountain.
The incident at Mount mang might just be a test by the sacred sect. Therefore, the sacred sect shouldn't be fighting to the death with the people of the righteous Alliance at Mount mang. This could be seen from the situation of the people at the Moyu.
The Alliance Army from Moyu had been confronting Zhao Hai's group at Yin corpse city for a long time. This was not normal. If the sacred sect really wanted to fight the righteous Alliance, Moyu would definitely send more than a few people. That was obviously not possible.