First of all, if MC had already known everything, even the perpetrators and their hideout, he could have went into their hideout and kill them all without waiting until they attacked first, much less until Labyris got kidnapped.
He should also abuse his time magic to go directly to last bosses or biggest villains and assassinate them, because him assassinating anyone with time magic would have been ridiculously easy... if he doesn't like to pose and hear himself talk so much.
But if he do that it'd be a literal RTA and the manga will end in one chapter.
![huh :huh: :huh:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)