I think I get it now why his best job is to become Ruby's servant.
Literally all his aspects are catered to Ruby's Demanding Needs ... Therefore, the resulting skills that he has is basically top tier... From Magic (protecting her), Gathering (even tho it's is only 40% he gathers ultra rare goods with it) even to downright cooking He is that good.
Him almost being good at everything is because of his job. That said, it doesn't mean it totally controls his life (like Shin Yuusha Nakama manga).
It be like The Guild master one... She could make a bread for herself and that bread will be delicious but it doesn't mean she will turn into a baker entirely.
On first glance, Being Ruby's Servant as Top Job seems unlucky... But the Unlucky one here is Ruby. Why? He is the only person in the world that can Satisfy her. She really shot herself in the foot with this one.
What a refreshing way to make someone OP... Just because someone is ungodly demanding....