(anon from first reply) Those certainly aren't bad ideas, but I do think the focus with Maria was less the challenge but, as you said before, the lore. Not even that, necessarily—the fight is designed to make an impression, which I think it does strongly? Not a beast or elevated being, but just you and another hunter, albeit one of vastly superior skill, and whose very purpose as a comforting saint has been cast aside to act as a steadfast knight. That's likely why she feels more like an NPC, after all. To me, I think involving any other characters in her battle would detract from the significance of her place in the story. I hardly think she would accept compatriots given her will to hide the secret of the nightmare.
I can't really say anything to argue my opinion of the music since that's entirely up to opinion, but I think it at least captures her desperation. After all, she despises sanguimancy, yet resorts to it in a last-ditch effort to stop you. It even matches with her more aggressive grunting and shouting, which seems uncommon even for Souls characters. There's sadness, fear, and anger all at once.
Bloody Crow is... okay, I guess? I just always bait his dash attack and riposte until he dies lol, so he's not exactly a challenge once you figure out how to exploit his AI. He also has the least backstory out of the entire game, if he's even anything more than a conjuration of Eileen's psyche.
But thank you for clarifying, it's still good to hear others' interpretations. At least Friede kind of fulfills some of these proposals in DS3.