I'm not convinced WEBTOON takes action on anything 'borderline' unless someone actually reports a page; it's pretty unlikely the mods will come across your work on their own unless you're promoting the bajeebas out of it, and using all the right #'s and @'s on Twitter and Instagram. Or it blows up and regularly cracks into the CANVAS Top 30 lists.
Your characters are also so bright and stylised, you can probably get away with their cleavage outfits. (Which look amazing, by the way! Great character design.)
You'd be able to get around it with minimal design change by adding a skin-tight bodysuit under the dress fabric, and removing some of the lines defining the cleavage. But I can totally see why you'd rather not bother.
Maybe speak with @carloswebcomic? His comic, My Pet Succubus, is actually ecchi, that's what the comedy of it hinges on. I was really surprised to see that most of its episodes are on WEBTOON. It also has a big readership, enough that I'd be enormously surprised if the mods weren't aware of it. He'll likely have some valuable experience navigating this line.
