If you've read my posts in "myth or reality" you'll be familia with what I say when I agree with what Diantha said about Merlin maybe not being his real name. In the book we were talking about, the authors said they believed Arthurs name was something to do with a bear (Arth/welsh) and (ursus/latin from memory) which I cant remember what that meant. But when they went in search of Merlin or someone like him around the same period as the person they believed was the real Arthur, they obviously never thought of Merlin being a nick name like they considered Arthur (Arthursus) to be. Such animal names were often and only given to a select few brave, or honourable, or influential persons, like Royalty, if in fact merlin was of noble birth. (bastard beast offspring or not) I think Diantha may have a point worth following up on.

As for all the christian tales. Taking into consideration that most if not all the early "reports or stories" were written down by Christian monks, they probably dont make for accurate accounts of the facts as pertained in modern abstract history.
Besides, theres a good chance the majority were still pagans at the time.