Okay so from my understanding, these 3 apprentice gods were basically like "yay human supremacy, here's the tools to stay in power for effectively eternity"(either being a really bad experiment or something intentional) giving the king and the high mages the big stone(i don't remember if they...
If the firepower is too strong it reaches the intestines and destroys the elixir, basically they need a reliable and relatively low power way to deal with them to not damage the elixir. The burning team is probably for a more controlled approach, having a lower power than fireball for example