Just keep in mind: Mialee doesn't look secure about herself. She doesn't look that she could go alone in an adventure. Even her Epic Level portraits show us a weakling: Weak arms, weak torso, weak eyes...
Seoni isn't Amiri, and she isn't Valeros: She cannot bend iron with her bare hands. But she looks like she knows her limits, and doens't have any fear to test them.
That's the difference, and that's why Mialee doesn't look like an adventurer, and Seoni does.