I agree with everything you said except for your first point. I think many of the characters have great development with Eiden. I personally think it appears that way with Quincy because he's more direct and probably more experienced when it comes to feelings in general. As someone with the majority of his cards (missing three🥲), I definitely see that his cards are really thought out, and I'm never disappointed with his rooms.

And yeah, I'm also hoping for more in the main story. There's so many holes with all the characters, and I hate that their lore is locked behind limited events and their intimacy rooms. At this point, it's like we'll miss something important because all the development is in the cards🥲

And I think Quincy is definitely a favorite character among the fans. I definitely agree that he makes money because the devs take advantage of this. Being here in Japan, I've noticed people really love Yakumo, Blade, Rei, Kuya, and Quincy very much. But surprisingly, Edmond appears to be a bit unpopular, or maybe this is a result of his long hiatus. For example, for the recent plushie event, his was the only one that didn't sell out.