The use of vessels by gods can be likened to the use of Accumulation by demons to reach the power of a demon lord. It is not a sustainable option and it cannot compare to the real thing. Vessels can't use the full power of a god. They will die if it is tried so all those vessels will probably die too.
Even Stelios's zealots will not be able to hold back the demon king for long. They both have Authority but Stelios's vessels will break first before the demon king and they will break easily too. The vessels of the other gods are sourly lacking. They wouldn't be of any use at all. So the liberation army is being sent to their deaths.
The gods would have been nonchalant about the loss of an army in the past. But believers are scarce nowadays. Believers that are willing to die for their gods are even rarer. These types of believers should be taken care of and used as seeds to grow their church but they also need to eliminate the demon king or there won't be any chance for their church.
Most of the soldiers are fighting because they believe they are doing the right thing not because they believe in their gods. Zargoth plane is their home and it is being terrorized by demons. They have seen the destruction and the death that has been visited upon their home. So they hope to beat back the demons and restore peace to their plane. And yet, here are the gods throwing them out as cannon fodder to buy time.
The god of knowledge doesn't care about their lives, it just pains him to see good sources of faith go to waste. If it were up to him, he would have decided to send Stelios's zealots alone to face the demon king. They are stupid and above all, they are not his believers so he won't care if they die.
'It is all those demons' fault. They don't think about the future at all.'
Demons and gods are enemies. They usually target the same thing but they do it with different approaches. Gods are after faith which comes from believers. They tend to their people as one tends to a flock. They kill a lot of them sometimes for entertainment or divine wars. But they make sure that their source of faith is sustainable. Moderation is key to gods.
Demons on the other hand just kill and kill without limit or care. What they want are souls not replenishable sources of faith and they need to kill to get the souls they want. They will harvest everything that there is to harvest and then return to the abyss leaving the plane in shambles. If demons had long-term benefits to be had for sparing people then they might be able to work with gods.
Every god agreed with the decision to sacrifice the soldiers no matter their gripes on it because what Zernon said is right. The GodSlayer takes a long time to load and is expensive, certainly more expensive than some mortal lives. A single shot is more than enough to kill the demon king and destroy the stronghold. It is like killing two birds with one stone.
Reloading the GodSlayer after shooting it might bring up problems. It wasn't designed to use Celestial Authority. It can use it and even use two of them because of its sturdy design and capacity, but it is uncertain if it will be able to use Celestial Authorities twice in a row. If the demon king leaves the fortress they will have to choose which one to target. It is best if they eliminate all their problems once and for all. So they had to send the Liberation army to keep him at the stronghold.
Back To Aeternus.
While the gods were preparing to annihilate him, he was admiring his new body.
"Everything has changed." He said in awe.
For the first time since he became a demon, he finally has a body. It is not flesh and blood but it isn't just bone with atrophied muscles anymore. He has real muscles now. They are made from his new authority of chaos. His body was heavily warped by chaos and will usually ooze out black chaos fumes but that has changed now that his chaos Accumulation has become the Authority of chaos.
He doesn't have any skin on his body. He has a layer of hard crystal flesh over his bones. His golden bones can be vaguely seen through the red crystal. There are some protrusions of bone around his shoulders, elbow, and knees revealing the golden bones but he isn't oozing out fumes of Chaos energy anymore. He finally has full control over his chaos energy now that he has Authority over it.
Having his body made out of his Authority means his body cannot be hurt by anything without Authority. And if his Authority is higher, the attack wouldn't hurt him at all. It isn't much of a boost right now since he has only one level of Authority but it will be helpful in the future once he has more.
His body changed a lot but it is his soul that experienced the largest boost during his evolution. His soul has completely healed and can match Legion-1's soul now. There's also a golden crown surrounding his soul. The crown is indestructible and will protect his soul from all harm unless the attack is backed by Authority. Even then, the crown will whisk his soul away to a resurrection point when his soul incurs too much damage. That resurrection point is usually the abyssal plane that they created or in the case of kings of the abyss, they resurrect in the 1st abyssal plane.
This mechanism is what gives the illusion of immortality to demon kings. It isn't true immortality because the soul will become vulnerable and can be killed if the crown is forcefully taken or lost. But apart from that, they can always return from death. As long as their crown is with them, they can always create another body for their soul.