Eh, King Alfred the Great and the resistance to the Danes probably were a major component of Arthur's legend. Caught one flaw though: two men, both obviously warriors to the bone, and only one of them is regarded as a knight. It wasn't until after this era that knighting was required; then, a knight was any man who fought as a profession. (Hence, the medieval Latin term for "knight" was miles; and knight itself originally meant manservant (and before that, boy).)
And was remembering how Poul Anderson had taken his hero and plopped him the middle of the Matter of France -- in an alternate history. It would make a lot more sense for the Matter of Britain setting to be alternate, too, what with plate armor and wandering Saracens during the same time as the Anglo-Saxon invasion. The closest I've seen to this is Vera Chapman's work, who used a lot of the tropes from Mallory and the rest, but even she smoothed out some for historical issues.
Same with Robin Hood. Friars were not in England in the days of Richard the Lion-Hearted. Or even in the days of King Edward ("Edward our comely king", which ever one was meant in the first ballads recorded of Robin Hood). Problem with legends, all the anachronism it accumulates. I still remember reading the Tudor era Robin Hood ballad having him appear before King Henry and Queen Catherine -- probably the Eighth and of Aragon -- and remembering how Howard Pyle had smoothed it into King Henry and Queen Eleanor.