Of course, one who needs to use AA methods isn’t, chash veshalom, doing something christian – he’s not praying to yushke, or submitting to him, or even serving Hashem the way they would lehavdil. There’s no avodah zara intrinsically in AA methods, rather a mistaken idea that humanity as a whole and every milchemes hayetzer is to be fought that way.
But he is copying one element of how Christians view humanity as a whole, while really they’re only correct about people with a specific mental health condition. Many false religiona take an idea that’s limited and apply it too broadly.
This is why i disagree with rabbi twersky z”l. He seemed to want to incorporate this idea into the mainstream, seeing the success he had with addicts. He meant well, but that is not the mesorah.