Mu Xi is indeed a playboy Little Overlord, but precisely because of his illustrious birth, he knows all too well what lines must not be crossed, lest even his uniqueness becomes worthless, potentially dragging down his entire family with a single misstep.
Like the trap Yu Changkong laid out, claiming that all lands under the sky belonged to the Mu Family—if he, in a moment of folly, agreed with it, any cunning person reporting it upwards would make Duke Cheng'en Mansion seem intent on rebellion. And once it reached the Holy Emperor, the brother-in-law, wouldn't there be a seed of doubt and a sliver of suspicion sown, even if they were believed?
Once the seed of doubt is planted, watered a little each day, it will sprout and take root, growing into a sapling or even a grand tree. By then, both Duke Cheng'en Mansion and Marquis Wei Guo Mansion would be in grave danger!