I agree up until the last point. At the core, the characters are still caricatures, as I put it, that are simply worded well. To me, good writing means depth of character that is fleshed out properly (and I don't mean spelling out everything, I mean giving enough characterization to each character, along with leaving some mysteries to grasp).
It is my belief that, despite the rough presentation, Final Fantasy XV actually has a good story underneath. The presentation is rough, the game had to be forced out, so we get something that is only a partial representation of the vision. This is actually much like Final Fantasy XII. I would actually say that they are comparably equal games in quality, they just have different positives and negatives, and one person might like one quality more than the other.
For example, the hidden lore of Final Fantasy XV's world I find more compelling than almost anything in Final Fantasy XII, despite the latter's better writing quality and presentation. The mystery of Ifrit, told subtly via the dungeon and other subtle cues, in my opinion, gives more depth than what I have witnessed in Final Fantasy XII.
But I'm not really trying to say XV is better. XII has a better developed world, with more of it represented in front of you, and the writing quality is generally higher. However, no questions asked, Adryn is many times a better villain than anything in XII.