Garen had a feeling that, ever since he started using the void crystal to confine himself, the muscular structures of his body had started becoming, leaving his body in a state of a suspended animation.
Even he himself did not know how his body is continuing to exist, neither did he understand why his body was being confined. He just understood that his willpower could still go through a Dream Weave. His hypothesis for this was that the essence for Dream Weaving is of a higher level the essence for confinement.
The superficial confinement essence that Garen knew could at most dispel some of the other average Regent Levels' essences or be used when conversing with the White King. Only when he was facing a non-Regent Level existence could it have any obvious effect.
When facing an actual Regent Level, it would be extremely underwhelming.