It is how normal transcendents should behave after they die. But the corpses of the behemoths remain and have littered the ground all around. If the Colossus were hated in the ancient battlefield because of their impetuous absorption of origin energy, Behemoths are loved because they don't drain Origin energy and because they leave behind materials for Origin weapons when they die.
The third and hidden option is when it is a demigod that transcends. The divine power within them fuses with their body and allows them to continue using runes. They can only use runes that match their divine power but it is still an advantage. Priests are stronger than giants of order in the mana stage because of the superiority of divine spells but that changes as transcendents.
Demigods are so powerful that they are more powerful than both Colossus and Behemoths. The body of demigods behaves like that of Colossus and Behemoths. You can cut off body parts to use but those body parts disappear when they die. That is why he needs this special Behemoth alive as he prepares his body for what is to come. But that isn't the reason why he is after this particular demigod that looks like a behemoth. He could have found any demigod to use but he wanted this particular special Behemoth.
Demigods are very rare because of their low birth rate and because most of them die trying to fulfill the requirements of heroic feats needed to become divine lords. Even rarer than demigods are children of Celestials, like the behemoth that Helios is butchering. Other gods give birth to demigods, but a Celestial gives birth to landed gods.
Landed gods are gods without divine kingdoms. They can roam the mortal realm but lack the protection and authority of a divine kingdom. You won't be able to tell a landed god apart from a vessel until they exhibit certain traits. One such trait is using the Authority of a god.
These landed gods created from a Celestial are rarer to encounter than Origin essence. They are very rare for various reasons. A true God cannot copulate with a mortal while two gods can't conceive together. Only a demigod, one that is part mortal and part divine can help conceive the child of a true God. That is a tough requirement.
Conception as a result of copulation between a mortal and a god is very difficult. Conception between a mortal and a god of the race of giants of order with low fertility is extra difficult but possible. Conception between a true God and a demigod of the giants of order is next to impossible. The chances are so low that any resulting conception between a god and a demigod is officially a miracle.
But that is not the biggest problem that limits the number of children of celestials. These landed gods are born with a divine ability like any demigod, but instead of using the small divine power that they gain from their divine parent, they use the Authority of their parent. This access to authority is not freely given either. It is more like they have equal access to the Authority of their parent.
In a nutshell, Half-celestials are born to usurp their parents and will achieve it if they become capable of wrestling control of the Authority away from their divine parent. So a celestial usually kill his or her child as soon as it is born. People are selfish, they don't like to share, and the gods are more so. No god will want to leave a real threat to their Authority alive.
Celestials had to struggle every step of the way to acquire their strength but a half-celestial gains their Authority simply by being born. That is unfair. The combination of fear and jealousy leads to the murder of a lot of half-celestial babies. It is a miracle for a half-celestial to be conceived. It is another miracle for them to survive their childhood. That's two miracles needed for one to encounter a half-celestial. It practically borders on delusion for you to hope to encounter one.
Some foolish celestials have been known to swallow their kids to prevent that future. They are too soft to kill the baby Half-celestial outright like a smart person. It has been shown that it is a stupid idea and it will not solve the problem.
The half-celestial don't die in the stomach of the Celestial. Instead, they gain access to the Celestial's infinite storage of divine power and grow up big and strong. Then they bid their time and take over their parent's Authority when they are weakened.
So swallowing a half-celestial doesn't remove them as a threat just like avoiding a problem will not solve the problem. Destroying the problem is certain to end the problem. But the Celestial Supreme who is known for his control issues and refusal to share power for some reason didn't kill this special behemoth.
This Behemoth is a true giant of order just like Helios is a giant of the sun. They both have access to the Authority of a celestial god. This behemoth was born with the divine power of order. So instead of the divine power weakening the effect of the law of order on his body during his breakthrough to transcendence, it enhanced it to great lengths. That's why he is the only one to survive Helios's decimating attack and the major reason why Helios is butchering him for a demonic sacrifice.
He might look like a normal behemoth but the other behemoths couldn't survive the attack even though the Celestial Supreme ramped up the god fire to empower them. They all died because no matter how much power he gives them, they don't have his Authority.
They need that Authority if they hope to match an attack that is equivalent to the power of a Sovereign and is catalyzed by the Celestial power and Authority of the sun. No amount of power can stop his attack without an Authority of equal level. This Behemoth hence filled every checkbox for preferred offering. He has a Celestial Authority, he is a giant of Order and to top it off, he is weak. It is practically divine providence.