The "allergy" AA speaks of refers to the abnormal physical reaction (caused by variations in alcohol-metabolizing enzymes) an alcoholic has when they take a drink. Some people are born with it due to genetics, for others it takes a long time to develop as physical tolerance increases and kindling occurs. Either way there's nothing mystical about it, it's a guaranteed stage of progression with continued use for any and all types of alcoholics.
Bill may have been open to other forms of spirituality but I don't think that applies to the Oxford Group. Although I've been trying to tell people for a decade that Christianity originally stemmed from what's now considered "the occult" and paganism. Most religious folks won't entertain that idea, any more than I see their gospel as being open to alternative interpretations.
There are also Biblical references in the BB to the Four Absolutes and the Book of James. Knowing these facts has actually made it easier to accept the religious aspect, because without an explanation or understanding the history it’s always seemed to me that AA is pretending to be something it’s not. Or pretending not to be something that it is.
If the history were openly disclosed, the common practice of saying the Lord's Prayer were eliminated, and the spiritual lens through which AA views alcoholism were updated to include modern scientific knowledge, I could almost see the religious aspect becoming non-contentious.
I never thought I'd get this deep into it but this is where my own recovery has taken me as I'm nearly finished with the addiction portion (designed so even non-addicts can understand it) of the academic program I'm still in. And I've been cutting back on my posting here but dropped in just in time to see the re-surfacing of this topic lol.