Jason being a veteran is doing more work than anyone is giving it credit for

It explains the competence without making him a criminal by nature. He can handle a weapon and stay calm because somebody trained him to, not because he grew up shooting people.

It also explains how he ends up working for smugglers. Somebody with those skills and no plan is exactly who that work finds.

Every other protagonist in this series was already a criminal when you met them. Jason is a person who was pointed at something once and never got pointed anywhere since.