Like Father Like Son.

His attack with the Celestial Authority of the Sun separated the useless chaff from the grain. The attack required a Celestial Authority to survive. He would have simply waited for the Celestial Supreme to send more if that attack had killed every single one of them. Fortunately, he got what he wanted on the first try because the Celestial Supreme decided to go all out from the start. Now he gets to use the behemoth for the glory of Legion.

To be precise, Helios needs his flesh and blood because he has the Authority of Order imbibed into his body. He can ask the screaming behemoth nicely for his help and skip the butchering but why bother? Asking for help will allow opportunities for mistakes and failure. Failure cannot be allowed because it is another clone of Legion that is at stake. If you want something done right, it is best you do it yourself. So Helios will sacrifice this behemoth to the will of the abyss with his own very hands.

Above In The Divine Plane.