It seems to be highly useful, but I reckon it's not tied to the level, perhaps only intelligence, experience, and hard training. It's pretty weird how such a thing isn't more common, but then again, most adventurers don't try to descent to the deeper, more challenging floors and can get away with less. It alone certainly woudn't give Lefiya a power boost, though, as her uselessness makes her only level 1 equal, no matter how great her theoretical power or the unique skill.