When Luke was asked to head the Shadow Squadron by Emperor Callant himself, he felt honored. Still, he did not accept to be the leader of something so important.
Yes, he knew that he had his merits and efforts that made the proposal not so lunatic. However, Luke knew that everything he had learned in the last year was not enough to command a squadron, because he didn't even feel like a leader.
The half-wolf felt that if he agreed to lead a squadron, the lives of all the people under his command would be in his hands, so he agreed to just be part of the Shadows and follow some orders. Luke knew that he was too involved in the war, and that now that it was on, he couldn't run away from his responsibilities, not least because he had people to protect and a home to look after: Oukiwa.