I suppose it depends on how clear-cut you make the "real person" piece; after all there are a great many fantasy novels that take into account Arthurian mythology (Celtic and traditional Arthurian mythology is all over the place in fantasy, it seems to be the source of choice). And of course there was all the Celtic stuff that floated to the surface for a time.

On the other hand, the two series I like from that age, The Romance of the Three Kingdoms and Outlaws of the Marsh read more to me like proto-fantasy in that they are written more like novels then most of the other pieces of mythology and folklore that I'm used to. They're also much more coherent from story to story. I'm not sure what that makes them; it's just hard for me to categorize them quite in the same way that I categorize something like The Tain.