Sexualizing teenage girls is not negated by also sexualizing teenage boys, though you really misunderstand what the concept of sexualization even is if you think the balls thing is relevant here. Sex gags are often used as an excuse for sexualization, but the balls plot and associated jokes are clearly not.

You are furthermore making up bizarre criteria to excuse the base facts of the depiction. Whether the women are helpless for the entire scene is completely immaterial, there are countless smut manga that are just as if not more disgusting where the woman does (eventually) escape of her own power.

She didn't need to lose her shirt to "make the threat more real", that was done purely for the viewer's pleasure.

More centrally to your comment, I'm not saying that Dandadan and Goblin Slayer are the same thing, I'm saying you are engaging in the same fallacy that Goblin Slayer apologists are, acting like something cannot simultaneously be eroticized and narratively "bad." In many cases, those two things can be closely interlinked, because something being narratively "bad" does not mean that you do not, on a meta level, want the viewer to not enjoy it. That's not how stories work. The Alien is meant to be scary, but it is simultaneously meant to be cool, made more obvious in the way it basically became a mascot in later enstallments. At the end of Rogue One, Darth Vader slaughtering the rebels is narratively a grim event, but it's very clearly fanservice in the broader sense because it's simultaneously meant to be enjoyed as a power fantasy of an action scene watching him carve up and force choke a big group of nameless opponents. This idea that every scene means only its explicit narrative depiction from the protagonist's perspective is like hearing the words someone says and assuming each word is exactly what it denotatively means with no nuance of connotation or innuendo.

If UT was still with us, I have faith he would say: "The curtains are blue".