Step 1: Realize that everything we know about Legendary Pokemon is based on mythology and guesses.
Step 2: Realize that everything we know about Legendary Pokemon is based on games, cartoons, and comics made to be child-accessible.
Step 3: Realize that any serious discussion about Legendary Pokemon can be nothing but flawed.
Step 4: Order some Pizza and take the day off to recover from the mind you just dun blown.
Honestly though. The just made crap up cause it sounded cool as a Pokemon. Creator of All Pokemon. Ancestor of All Pokemon. One's a superstition. One's a theory. They can get away with it because they're never in the same story (Has Mew had a Game story arc?). Neither is right. Though, my Logic side has to say that the theory is closer to being right because they have DNA to back them up. DNA>>>>>>>>>>>>>>>>>Cave paintings and folklore :D