It's not easy to dump or dethrone the red head empress because her family is much powerful, that's even the reason why the late empress begged the emperor to marry her . Their influence is much greater than the royal's,they even have the magic tower. Only the grand duke defy the empress,if you noticed no nobles or no one adopt FL even in her first life. Shushu will have both surnames of her fathers
From what I feel, the emperor may be intelligent but he feels very naive thinking there will be happiness when he retrieves his daughter, he has the emotional side of a mother due the loss of his child and partner. The duke feels more levelheaded, yes both of them will do anything to protect her but the one that plans ahead feels like it would be the duke and in many scenes I can see him throwing logic to the emperor and leaving him tongue tied again and again. So far from my bl experience it feels like Duke (manipulative/serious/hear-warming top) X Emperor (naive/impulsive/strong bottom)
The only thing that I want is for her biological father to dump the Empress and get together with the duke and have a blended family, emperor as a power bottom would be cool