The Sunne in Splendour and Maxwell Anderson's Richard and Anna (which I know is utterly worthless historically) are what did it for me. That is, Tey got me interested and on his side, but I didn't fall for Richard until later.

Yes Da Vinci is really the same kind of thing as Kushiel, but 1)Kushiel doesn't pretend to be more than fiction and 2)the writing in Kushiel isn't pathetically bad.