Cain's eyes widened with awe and admiration as he saw how Archduke Halbinder managed to not only face three Legends from the Lynch Kingdom simultaneously but also destroy the body of one. It was clear from the man's courage and battle will that he did not reach his position out of luck, but through immense hard work and bloodshed.
Every single death among the Legends of the Lynch Kingdom was a massive victory for the Trinity Kingdom, but Cain knew they couldn't be too happy. Up until a few minutes ago, Archduke Halbinder had been on the brink of collapse facing the trio, forcing himself to the utmost limit, yet now he was able to overpower them. That power-up was the result of the potion the Archduke took and something that could raise your strength so much so quickly was bound to have severe backlash.
Once Archduke Halbinder was no longer able to fight, the balance of power in the Legendary battlefield would shift to the Lynch Kingdom.