I advise that one DOESN'T watch this. Apparently the writers haven't done their research well.
I doubt that it's a matter of sloppy research. They just looked at the raw material, then did their own thing--which is what people have been doing with the Arthurian mythos for centuries now.
It's all just myth and folklore anyway. There are no true, definitive facts to adhere to. I mean, it's not like Boorman's EXCALIBUR, the Broadway musical version of CAMELOT, Disney's SWORD IN THE STONE, and Monty Python are all scrupulously faithful to each other. Heck, the whole Lancelot/Guenevere thing was made up out of whole cloth centuries after the fact.
This is just the latest variant . . . .