The sudden pain does, indeed, snap him back to the situation at hand. Every one of his many souls snaps to attention, pouring their focus and energies into the task of fighting. It's what he was made for, after all.

Ermac seems to blink out of existence, only to reappear behind Ellis, charging into him shoulder-first as he does so. Before Ellis can hit the ground, Ermac fires off three weaker blasts of spirit energy in quick succession; he has no wish to do any permanent damage to the man he still thinks of as a sort of ally.

"We fight for Outworld, as we always have."

To suggest he had any sense of loyalty to Panem was an insult.