I don't think TLT introduced a "Christian mythology" so much as it introduced a being who was in part behind a portion of Christian mythology. Not a whole lot different than what SG-1 did with the Egyptian gods, really.
To say nothing of the fact that we already had met a race who has fed and hidden behind a Christian Mythology for Millenia
Thirdspace has the benefit of giving Pat Tallman a lot of screen time, which is never a bad thing to me.
And there's the great elevator scene with Zack
One Day I hope to be the Man my Cat thinks I am
Where are we going? And why are we in this Handbasket?