One set of characters exists having personality evolution over the series with circumstances to govern their emotional state. This applies more to Ayane than Kasumi, but it does apply to both. Kokoro never had any development, but she didn't commit any real sins either. She's an airhead. Oh well.
Maire and Honoka never had any development, but their sins are defined arbitrarily. They're childish. Oh well.
Ayane was originally a minor villain who later evolved to be sympathized with. Tsundere would also be the wrong classification for Ayane, as she would have to have moments of warmness. The closest she gets is deciding to not hit Eliot. That makes her a bitch, not a Tsundere. Sorry to the Ayane fans out there.
She does have moments of warmness (see: Hayate with whom she becomes visually distraught any time he is faced with peril). You can be a tsundere and a bitch. In fact, that's true for almost every tsundere character.
Another set of characters exists as a trope with an emotional state and no circumstances. When they have no circumstances with which to justify their personality, they become less a character and more a trope. That's why tropes exist in the first place -- to classify shallowly written characters easily.
Well, first we should clarify that we're using 'trope" in the colloquial sense rather than the classical one. In this way, it's more or less a stand-in for both motifs and archetypes, but archetypes do not exist merely to classify shallowly written characters. They often work with core literary devices such as motifs (and yes, even classical tropes), many of which can work well, which is why they have been inevitably re-used across fiction over centuries. An archetype that doesn't properly evolve itself from a recognizable mold, in contrast, is a cliché or stereotype.
The line separating archetypes from clichés often varies from person-to-person as well as from character-to-character, but mere circumstance alone does not elevate a stereotypical character into being a well-written or idiosyncratic archetype. I can give you an example: if TN gave Honoka a shitty side story in DOA6 where she joins the tournament to search for clues about her parents but instead bumps into Zack, who hits on her so she beats up him by stealing his Zack Beam move with her magical, move-stealing hand, she'd hardly be any less of a bland, clichéd stereotype than she is now.
If you're about to argue "That would be better than nothing," I would reply "I suppose," but true nothing is almost impossible. Marie and Honoka do actually have some contextual backstory (as shallow, shitty and compelling as they are) behind their bland personalities. Kokoro is not really any different. Frankly, neither is Mila. The only difference is "screen time," but if that's the primary concern, you're in luck, because I'm pretty sure that Marie and Honoka are going to be getting more screen time if/when DOA6 rolls around ("yay").
Yet, Nyotengu is also a mega trope with hardly any backstory and I find her less offensive. Why? Because of the same thing I said in the last post. Those tropes don't bother me, and these ones do. I don't care about the ditsy-acting underage school girl (regardless of what the bio says) with oversized breasts who has nothing to do with the established setting and only exists as a reminder that Japan is Japan. At least Nyo is a monster.
This basically equates to: "All these are dumb, but I like these ones better than those ones, so I'm going to claim the ones I don't like are more dumb and/or poorly written than the ones I do happen to like."
I mean, Marie is frankly the biggest reminder to me that Japan is Japan considering how loli/anime-obsessed the country seems to be. Sure, it might bother you more than Kokoro, but to say that its dumber than Kokoro is, well, dumb.
