The actor told SciFiNow that the BBC drama should not be considered a "definitive telling" of the Camelot myth.
"We're here to provide Saturday night escapism," he explained. "People should not take what we've done as a be-all and end-all of the legend, because it's really not the case."
He continued: "It kind of changes the story because primarily [the show is] about... Merlin. You can chop up other characters' storylines, but as long as you're telling the story of Merlin, it's kind of okay."
He noted that the continued survival of Uther (Anthony Head) marked a large deviation from the original legend.
"We've changed so many aspects and really altered the story," he claimed. "Primarily, Uther still being around is a pretty big deal."
However, James insisted that he still enjoys playing Prince Arthur after three series in the role.
"It's still fun," he said. "I still tell people that I swing a sword around for a living. There's still many aspects of the role which, as a big kid, I very much enjoy."
The third series of Merlin concluded on December 4, with a fourth run already commissioned.