CC-Kun
There was a torrent of energy circulating within Stencil, a result of her newfound powers. But, they were also gradually waning in strength as they were regressing. As Stencil had expressed, only at noon—figuratively—would she be at her peak, and that was when her powers too were at their strongest.
Conversely, when she was a baby, Stencil was as weak as a newborn human baby. That was her most vulnerable state. The reason Regression went to the extent of sacrificing a level to unleash this attack was to ensure that Stencil would never grow to become a threat.
And it had indeed achieved it.
Irrespective of how the collective consciousness driving her worked and gained strength, they could only express the peak of that power for a couple of seconds. After that would be a steady decline of their power until noon of the next day.