Mu is changing. Turning into the DS Emperor, I think.
Going late game 4x mentally. Don't need to care about balance, just easier to purge. Likely the correct approach here, but it he doesn't get them all at once, no clan will be left alive.
They've been foreshadowing him following the path to becoming the modern day Lord Yufeng for a long time now, the wide scale massacres and clan exterminations to clean up Daxia were a long time coming honestly.
Like they said, the military advisor is really "so-so". What infamy? Yufeng was 10000 more ruthless, and the result? His clan became the #1 clan for hundreds of years. The Ditu Emperor massacred civilians in their multitudes, and even Daxians still look up to him. You're afraid of infamy? Just hire a good PR firm. Don't let traitors kill your people.