I've seen people say Lucanis' choice in his companion quest should have been whether to become First Talon or not instead of what to do with Illario, and I just don't think he’s at a point where he can do that yet.
He's been conditioned all his life to obey Caterina. He's just been tortured for a year, had to deal with nearly losing what is left of his family, and had to come to terms with being stuck with Spite (on top of fighting elven gods...). I don't think he's got it in him to fight Caterina right now.
Maybe in a few years, when things have settled down, he could, but I guess by then he's gotten used to it all and won't want to rock the boat by, I don't know, quitting the Crows to open a café? Or a restaurant? He's pretty much stuck with that job, it was never a choice he could make.
Illario even asked him in Wigmaker Job if he would tell Caterina "no" and he replied that he can't.
“And if Caterina disagrees? If she thinks you’re the better man for the job—”
“I don’t want it, Illario,” Lucanis insisted.
“But you wouldn’t refuse.”
“It’s impossible to refuse Caterina,” Lucanis admitted reluctantly. “Only prolong her, until she sees reason.”
So maybe if Illario hadn't messed up so badly Lucanis would actual have dragged things out and tried to make her see reason. But like this? When he's the only choice left? He was never gonna tell her no.
