Just two things about Principia Mythica, not really contradictory, but just to give solace to those who wish for a different Myth world view. While I found it to be basically satisfactory, I always like to spawn different views on these things, as it is the only way that satisfactory truths will emerge from our minds.
Okay, enough pretentious garbage. Here we go:
1) A journal entry mentions how, to Soulblighter, only a few seconds elapsed between when he trapped the Legion in the Tain and when they escaped and shattered it, while the Legion had been inside two days. This suggests that the Tain is not really a portal to some geographic location midway through to the Other Side, but really just a mini-universe. This more obvious possibility sparked a Myth world theory that will have its own post, as it is really a wholly differnt Line of Thought.
2) Principia Mythica does not mention the simpler possibility about Connacht not being able to find the Smiths of Muirthemne and their followers when he raided the base of the Spider Cult. Instead of the Smiths (who are probably dwarves) being the leaders of the Spider Cult, they may have been its victims. They might have been kidnapped by the Spider Cultists and had Connacht come to rescue them.
I have probably missed something important about these two aspects of Myth that I have pointed out. I would appreciate you pointing out any mistakes I have made.