Ben Warhol's page

Congratulations, you can quote the same line out of the same source that I did. That does not in any way address the question of what to do when the item IS an artifact, by dint of it being made one by 2-3 applications of Legendary Item.

The rules say that you can't put Mythic spells on items that aren't artifacts. Of course then the rules say you can go right ahead and turn Legendary Items into artifacts, but then turn right back around and fail to give you rules on actually crafting mythic and/or augmented spells into them. Quite irritating.

A lot of Mythic is quite decent, but Paizo dropped the ball in a huge way on the itemization and crafting side of things.