The Wealth Armament divine ability requires money, and a lot of it, to create its offensive and defensive means. Money is more expensive than lives and can even buy lives, so Blood Sacrifice has the advantage in cost of usage.
The advantages that the Wealth Armament divine ability has are that it has a lower barrier of entry and can be used to protect one's life, not just for attacking.
Blood Sacrifice requires a killer to be an angel to use, while the Wealth Armament can be used by epic merchants. Plus, Blood Sacrifice does nothing to protect its user.
Killers have always believed that the best defense is an offense. If they are going to die, then they might as well bring everyone down with them.
Legion had all the advantage in this ambush, but they didn't want to waste time fighting epic beings. They came here to advance, not fight, so they opted to spend a lot of money to end the fight as soon as possible.
