Good question. I discuss this at length in my new book Emotion and Art, soon to be posted on the site. If you're using your art (the writing) as a means to express any feeling, you're basically still in the "get it off your chest" camp, which I feel has limited therapeutic potential, maybe even suppressive, especially when the expression is accompanied by projection and blame, as you say.
The key is to shift to the place where you're using the art to experience the feelings, not to primarily express them. Your subtle intention is not to get rid of, but to be with. Then, the art can definitely help uncover the subconscious as you allow the stream of consciousness.
The shift occurs through awareness of what you're doing, your intention, and then using the witness to be with what is emerging. You also apply the steps of processing to the art experience, taking responsibility, etc.