It is true that with improving historical knowledge you get a lot less leeway. Once Scott started to write historical novels where changes between past and present were part of the novelist's bag of tricks, it spread outwards. Nowadays you have to figure out some way to translate it into the land of myth to work with it. And go all the way into the Land of Myth and Legend. Perhaps the writers decide to go all the way and chisel off the names as well as the rest of the identifying marks to make a Good King or a Good Outlaw Archer.
The irony with the nitty-gritty style is that one thing they never do research on, or any rate use, is the development of the legend. You look in vain for versions of King Arthur where Sir Gawain is his best knight, with Kay and Bedivere, and Guinevere is not adulterous, though Lancelot and Galahad, and even Tristan, were latter additions, dragging in courtly love and the Holy Grail with them. Or Robin Hood accompanied by Little John, Much the Miller's son, and William Scarlet or Stutely or Scathelock or Scarlock or Stukeley. Along with a great mass of undifferentiated merry men, here and there punctuated by names in different ballads (Gilbert Whitehand and David of Doncaster anyone?). Maid Marian is actually an older character, appearing as a shepherdess in plays and later May Games, but didn't appear in the Robin Hood legends until there came a fashion for Robin Hood plays during May Games, whereupon apparently there was a cross-over, and she stuck. (Not the first character to do so. Morgan Le Fey originally was part of the Matter of France, not Britain.) Friar Tuck also seems to have come from the games. As for Allan-a-Dale -- Victorian.
But any nitty-gritty realistic demythologizing version will be sure to explain the Real History behind all the characters that couldn't have been there.