Agree that some contemporaries are engaging in an anachronistic fallacy. But this paragraph is interesting:

“All of this is largely irrelevant to “history” anyway since King Arthur never existed, or if he did exist he would have been a random Britonic warlord some time in the period after the Roman departure who has since blended with some mythology, and with layer upon layer of complete fiction added on top until the result is something unrelated to any historical figure.”

Substitute “Jesus” for “King Arthur” and replace “random Britonic warlord” with “random Hebrew zealot” and it would be just as true.