Yes, in "a person’s value comes only from his or her sexual appeal or behavior, to the exclusion of other characteristics" the word "only" appears. And if that's all they looked at, I might agree with them. But they go further and say, "a person is held to a standard that equates physical attractiveness (narrowly defined) with being sexy" and include that as also being sexualization. And in that case you added the word "only" to change the meaning of the second sentence.

According to the study, having either the characteristics of the first sentence or the second sentence makes the work sexualized. But if we use the second sentence, any work that shows that someone is sexy because he or she is physically attractive is sexualization. That means that all the physically attractive women in comics, if they are shown to be sexy, are sexualized and harmful to girls.