Why not? I'm curious as to your thoughts here. I haven't read the Dresden Files, unfortunately, so I can't compare.
First off, go read Dresden Files. Just trust me. Book 1's good, Book 2's better, and Book 3 will blow your friggin' mind. And Michael (who appears first in Book 3) is what I wish every paladin was played like. He's definitely Lawful Good, but he's also definitely not Lawful Stupid. He has a strict moral code and he knows exactly what that code entails, but he doesn't expect others to live up to it either. He accepts people as they are including their faults. He may chastise them for it, but it's closer to a parent going "I'm disappointed in you" than trying to convert someone. He's much more "lead by example", proving that a holy and virtuous life leads to a good life and bringing more good to the world. The downside in D&D terms is, again, Christian. Which doesn't fit with pretty much any of the D&D pantheons.
And I think the debate on Arthurian mythology comes from the fact that there's just so many different sources and so many different stories. In some of the later versions which include the Holy Grail, there's a lot more of that ideal of Christian chivalry in the stories and it shows through in the knights. But in earlier versions (and versions that draw off those earlier myths), they were probably formed before Christianity was widespread in England. So the stories, even when they show some Christian influence, aren't focused on those ideals. Lancelot, for example, is still an expert fighter even after he breaks his oath to his king and friend by laying with his queen. I don't even recall ever hearing the story mentioned before about Lancelot losing his "miracles" after losing his virginity or ever having "miracles".
Galahad, though...that's my fault. I was confusing him with Gawin (who has a far more interesting story IMO). Galahad's a footnote in the pre-Grail stories, mentioned as being the most pious and virtuous knight but not much else is talked about. It wasn't until the quest for the Grail was added to the stories (pretty much with Troyes).
Honestly, it's incredibly difficult to talk about Arthurian myth because, like the vampire myths of Eastern Europe, they changed with the rising influence of the Church. They originally had nothing to do with the Grail or Christian virtues directly, but it was added in over the years, especially when the ideal of the "virtuous knight in shining armor" and idea of chivalry started to spread (which the idea of chivalry far post-dates the origins of most Arthurian myths). There's so many versions of the same stories that it's almost impossible to determine which one is the "canon" version as it just depends on the author at the time.
I can go into a lot more detail on vampire myths evolving, though, because it's something I've done more research into. Arthurian myths have only really interested me as the tropes they formed applied to the fantasy genre. But vampire myths really have nothing to do with this discussion except as an example of this sort of morphing over time.