Get a copy of the Big Book and read the founders' take on this. Bill W. and Dr. Bob were both serious Christians and had tried the prayer cure many times. Didn't work. Historically, religiously motived recoveries from alcoholism were rare enough to fall into the category of miracle cures, and they were certainly not clinically reproducible. (Or there would be few or no drunk ministers and priests, which we know ain't the case.) AA offered a technique that worked better than anything else yet devised.
Similarly, most of the other early AA's were also at least nominally Christian. (This was 1930's America.) Early AA was much more religious -- and overtly Christian -- than it is today. Over time however, as AA accumulated experience and developed a positive track record, it was recognized that plenty of non-religious and minority-religion folks became drunks the same way as Christians, and got sober the same way too. It was recognized that issues of religion should not be allowed to become an impediment to seeking sobriety.
The accompanying assumption was that progress toward sobriety tended to correlate with spiritual progress as well. This is true whatever the religious heritage and/or destination of the recovering alcoholic. Jews, Muslims, Buddhists, and atheists get sober too. The religious expression of any particular AA group will depend on the locality. That's all.
I think you are picking an artificial fight on this point. Go to an open AA meeting and ask about it if this still bothers you.