Its fine to point out the ills of bad men... but then also condoning lesbian sexual harassment as okay, fun, cute and comedic does not help the messaging of this manga.
It's like "Don't accept sexual misdeeds from men... but embrace it from lesbians, even if you're not one... just take it ... sooner or later you will become at least bi." No bueno.
Laplace has been a bit of a weirdo from the start, like she didn't ask Tanya before she kissed her either. But the idea that she would be "converting" Kathy is silly, since Kathy already fell in love with Nadine a while ago. And Kathy is not flustered because she secretly likes being sexually harassed by Laplace, but because she likes the clothes Laplace gave her. She is not "embracing" or "taking" anything.
I think you might see a morality lesson here just because the heroes are struggling against misogyny. What Laplace did can be considered sexual harassment, but it's also the kind of questionable horseplay that female friends might do with each other. It's taken less seriously because Laplace is a woman and a friend, not because she's in love with another woman (that logic wouldn't make sense, and Kathy doesn't know about it anyway). Since this is fiction, we also know that Laplace was not getting off on this, or exercising power over Kathy, but just teasing Kathy for still wearing her old battle gear.
Either way, I can see why this gag could be inappropriate for this arc, but I don't think it's a serious detriment. Its severity is not at all comparable to the topic of this arc (date rape and forced marriage). Most people can understand the context of the gag, and won't come away with the lesson you're supposing, which feels deliberately uncharitable.
It almost feels like you were waiting to catch the manga in a moment of hypocrisy because you have some kind of a vendetta against either feminism or lesbians. See, I can also invent a sinister motivation with flimsy evidence!