The first Sage needs someone with whom he can work hand in hand to improve the plane. Preferably someone that knows his will without him speaking about it. Someone that cares deeply about the plane and doesn't need to be baited or bribed to do something for the good of the plane. Someone that can be completely trusted. Soverick is not any of those things.
Soverick became the child of the plane because he had a use, and he can be removed when they consider him no longer useful. It is not because he is a bad child of the plane. No, it is the fact that there could be a better alternative. Soverick is on the path to becoming a world god, while Salvini doesn't have a definite path to that level of power yet. But Salvini can make that path possible. That's the difference between the two of them.
The Sage is particularly impressed with how Soverick controlled the overflow of power when he summoned assistance from the plane. It was his first time, but he got control of it perfectly. The Sage didn't have that kind of control when he was the child of the plane. He had to train it to get it. It was difficult, but he managed to do it because he could achieve anything as long as it is possible. That's the innate advantage that foresight grants you, which Soverick doesn't have.
Soverick is great and all. He is strong, and he is talented. But power means nothing if you can be bossed around. He has been pulled along the Sage's scheme like a mule. He is a pawn. He may be a very valuable pawn, but he is a pawn nonetheless. He could have asked for three requests from the Sage, and he would have gotten them if he insisted. He is that valuable, but he didn't know his worth, so he was taken for granted.
Soverick could have gotten four requests if he played his cards right, but he settled for 2. That wouldn't have happened to Salvini. She may not be able to predict the outcome of her words during a negotiation with a world god, but she can predict her emotions and reactions to what the world god would say if she said some things. That would have helped her to make the best of the situation. If something is possible at all, then Salvini can achieve it. Meanwhile, Soverick doesn't know what's possible and what isn't. It is a shame, really.
Besides that, the first Sage wouldn't have needed to convince her or bribe her with much since it is for the good of the plane. She can be trusted to always put the plane first. Soverick, on the other hand, put his self-interest and self-preservation first.
He can't be faulted for it since everyone does it, but it becomes a flaw when there is someone else who wouldn't have done it. It gets worse when he doesn't take full advantage of the situation despite putting himself at risk.
Soverick can't make the best of the situation, so he will be replaced. It is not done out of hate for Soverick or love for Salvini. It is done for the good of the plane. They don't need to kill him to do it, thanks to the Sage's ingenious plan, but it is best if they do so. It will make the person that his title is grafted to be in complete control of the title.
The first Sage remained calm as he thought about his plans. He didn't show any indication that he had a meeting with Soverick, and there's no way for his co-administrator to tell. The serpentine world god did find out that Soverick gained access to a core though. It is an event that cannot be hidden.
"Look at that. Your so-called champion finally succeeded in breaching the core of an arena." The serpentine world god grumbled to the first Sage.I think you should take a look at
"I see." The Sage responded without enthusiasm.
"That's all you're going to say? Someone from your side just breached one of the cores of the arena, and all you have to say is I see."
"What can I say? That I am sorry that my champion is so brilliant? That I am sorry that none of your paragons are talented enough to do the same? Or that I am not showing enough happiness at cheating you? Which do you want?" He spoke with the same bored countenance.
It is not the reaction that the serpentine world god wants. For one, it is not a reaction that someone that is sorry would show. Then there are those insulting questions. It made him angrier than he already was, but the Sage continued to fan his flames of anger.
The Sage said, "You know what? Maybe I shouldn't apologize for that first one. Soverick is one of a kind, after all. It is not your fault that none of the billions of Vipers in your plane are this talented. It is a shame, really. I mean for you. It is a shame for you. It is my luck to have someone as talented as Soverick on my side. As for you, it is a shame."
The serpentine world god couldn't take it anymore. "Bullshit. What luck? You obviously exposed him to your law before the competition. How else would he have cracked the law matrix? He was overly familiar with it right from the start."
The Sage shrugged. "Maybe he has been exposed to it. What would it have changed had you also exposed your law of order to one of your race that is a king of law?"
That made the world god pause. He knows the answer to that question, and it made him shut up. A king of law that is exposed to the law of order of a world god will have their existence overwritten. That is another way to say that they will die and cease to exist.