Except that is not what that verse says. It says that Scripture is useful in equipping the men of God for good work, which it certainly is. It does not even suggest that Scripture alone accomplishes that or in anyway perfects men.
Except that it DOES say that Scripture THOROUGHLY FURNISHES. What can be added to make something MORE THOROUGH, NL? Then it isn’t THOROUGH to begin with. Read the Scripture. Unless your Bible has been “edited”, and THOROUGHLY is “missing.”