Whatever Varian knew about Duke came from others.
Catherine respected him and wished to fulfill his dream of Centaurus' revival.
The Imperial guards had a mix of opinions but most of them were less than supportive of his passive stance towards the drug mafia.
The Duke could've gone ahead and ended the Havocs himself. But he feared the unknown dangers that it could entail. What if the Havocs had a method to kill him?
Duke Cassius failed miserably in curbing the drug menace and watched it devour the people of his duchy bit by bit. Despite being the only person with the highest chance of ending the suffering, he chose not to act.
Why did Centaurus have to suffer for decades until an unknown man save it? If they needed some nameless savior, what good was the Duke even for?