@Kayriel I don't think you understand what Nadare is saying. He's saying that Kogarashi might turn evil and be unstoppable in the future, just like what Byakuei did in the past. How many people died because of Garandou's summoning by Byakuei? People died because he was too strong and made something devastating. Nadare himself can be stopped, he himself said that in the chapter. 10 Tenko is enough to stop him. But Kogarashi is way beyond that. What if Kogarashi really turned evil? He's merely taking a precaution.
But of course, this is all shit because Kogarashi is the MC. But from his PoV he has reasonable reason to do whatever he does.
Well, at least in this case, the initial reason why the MC is going to lose for a bit is because his spirit literally can't keep up with the spirit power. So, less because the MC wasn't trying to finish him, but because he can't without killing himself(potentially). Still a cliche, but that is something pretty much impossible to avoid now in storytelling.
That's not at all what it is. It's not about good or evil. It's 'you might decide the Tenko should stop existing'. As I said, he believes his family to be an absolute existence. He hates that he's restrained by his family, hates Kogarashi's freedom, the fact he's strong enough TO BE FREE, instead of being one of the many pawns of the Families in their stupid supernatural war. But also seems to revere or worship the chains that bind him, and uses them as the basis for his philosophy. This is purely jealousy and self-interest colliding in a tantrum against the MC. Nothing so grand and noble as you suggested.