You're right. The characters are only as smart, strong, diligent, etc. as their rivals. Even if the author tries to make us think that said character is a genius, we can tell what the author really thinks of the character by who they are set across from.

I hate main characters that are idiots. When the character does something spectacularly stupid, I see it as the author not spending enough time on the plot. Otherwise they could find a better way to advance it.