I feel the like the huge shift was the point, and it works from a narrative standpoint when you consider Jack's mental journey.>first few episodes are grim and dark, reflecting Jack's hopeless existence and mental instability>4-6 he and Ashi get closer, the show gets more vibrant, and the pacing picks up because Jack is actively working towards something again instead of wandering around "like a mad fool">Jack defeating the Omen and his inner frustration returns him to his original self, gets him back the sword>by episode 8, Jack is basically just like who he was in the old show, only now he has an attractive companion he's starting to notice now that he isn't plagued by visions>at the start of episode 9, he's starting to feel like he can be hopeful again, but his conscience warns him against relaxing too much>Ashi gets possessed, Jack is lost again
I'm really curious to see where the final episode starts off, as everyone expected 9 to be post-coitus but instead we got a direct continuation of the end of 8. But I digress...
My point is that the tonal shifts throughout the season are meant to reflect Jack's mental state, and it's slow recovery, with Ashi's help. Her importance to the progression of the story is I think the biggest evidence of her survival. I sure hope I'm right, but we'll just have to wait and see I suppose.