The antonyms for "more steel-plated" could be "less armored", "less fortified", "less protected", "less shielded", or "less reinforced". These antonyms describe a substance or material that is not as resistant or tough as steel, and is hence more vulnerable to attacks, impacts or damage. For instance, a wooden house is less armored than a concrete one, and is thus more prone to break-ins or weather damage. Similarly, an unguarded car is less shielded than a security-patrolled one, and is hence more susceptible to theft or vandalism. Therefore, antonyms for "more steelplated" suggest a lower level of protection or security, which could be either intentional or unintentional.