Everything happened instantaneously. Gravis freeing himself from the suppression, the summoning of the emblem, the breaking of the emblem, Gravis pushing all his Energy into the guard, all of this happened in the blink of an eye.
The Core Disciple and the new arrival couldn't react to the sudden and shocking actions of Gravis. None of them had even entertained the thought that Gravis had a chance of breaking out of such a powerful Will-Aura.
The breaking of the emblem would make it much harder for them to act as they wished, but it wouldn't be too bad. Someone at the Mid Minor Circulation Realm wouldn't be able to summon someone really powerful. Additionally, the person would take a while to come. Until they arrived, the Core Disciple and the new arrival would be long gone.