He could get pretty famous setting up shop as a trainer mercenary. Charge a fee to parties in exchange for helping them level up faster and more efficiently than other parties around them, while also using his eye skill to help the party focus and building up their strengths or overcoming their weaknesses that they themselves may not even know about. Obviously I know that's not what this series is about based on the title, but still. There'd be no real sense of companionship so he wouldn't be considered "dead weight" once they get stronger enough, since getting them to that point would have literally been his job. Once that's done, he leaves and goes on to help the next paying party.