Joshua Dalzelle i.e the author of the story has given a difficult assignment to Jason Burke and his men because they are fighting against someone who knows about them completely. It is like fighting your own shadow and Jason has finally received the most difficult assignment at last. Missions in Iron & Blood and Omega Rising were not that difficult because in those stories the main characters were fighting against an enemy.
Here the crew is fighting against a dear one who used to be their friend but he calls himself Seven now. Even if they succeed in reaching him still many of them would not be able to kill him. Perhaps this is the main reason that Lucky is alive and he has been able to kill that many people.