The front lines were struggling. The barrier had one key disadvantage compared to normal arrays.
It was based on the guards, and not array flags or something like that. And so, when an attack came toward the barrier, the guards had to expend their own Qi to resist that attack.
But what these guards were doing, it was just temporary. The Imperial Palace wouldn't have such a shoddy array as its main defending array. If this was the main defending array, then it would be a shame.
The Imperial Palace had a much better array, but it also took a lot of time to complete. And the palace knew that they would need a buffer. These guards were that buffer.
A few minutes worth of buffer so that the true barrier could be put in place. Multiple Soul Evolution Stage cultivators, led my Tian Hun, were in different parts of the Imperial Palace, getting the protecting array together.