There is no such thing as he was likely holding back. It wasn't shown or explained that he was. Therefore, he wasn't. This is fiction, nothing exists unless it's in the writer's intention. Writer's intentions are usually clear and clearly shown. Superman punched with might on his face. He couldn't be possibly holding back.
More trained that Clark has no bearing on her matching his strength.
Kryptonians are virtually immune to each others punches and most attacks, even HV. It's like one character fighting two characters when no one can hurt the other.
Also, Nam was getting the better of Clark. Clark never fought them evenly because of this.