If Legion-5 dies in the blood crucible then he will at least get something from his body. But if Legion-5 survives the blood crucible then it is almost impossible for him to die until he becomes an Origin god. It will be too late for him then. Unfortunately, he doesn't want to cross the Supreme Alliance so he can only watch his chance slip away.
He said to himself, "His mutation is probably nothing. It is unlikely that it will be significant. There is no need to stress myself on something that might turn out useless."
He said that to help himself give up on his motives for his son. It is self-deceptive but it is likely true too. Legion-5 is not the first mutant that he will encounter in his mission as the guard overseer of the plane but none of them have amounted to much.
