To be honest and fair, the whole scene with KC getting his weight increased is probably a non-issue.
First of all, we find out that he had a reason for busting out and it involved saving a girl. This means that he was clearly interested in keeping others safe, same as Supes always has.
Second, there is no way any of those characters or Starmans attack could have brought KC down if he didn't let them.
Finally, with his weight being increased and all, and nobody getting crushed beneath him, or losing a limb, etc, I would just chalk it up to KC doing everything he could to keep any of them from getting hurt, while still getting away in time to make the save.
Just my opinion.