It is not really about the 1930s. 1939 was when the big book was first published. Nobody knew how it would go. It could have failed completely. The reluctance to change it comes from how phenomenally successful the book was over the next 16 years. The fellowship grew from 100 to over 150,000. Just play with those numbers a bit and you can see how busy those early members must have been.
But it wasn't all one alcoholic working with another. In New Zealand, AA was started by one man with a copy of the book. It took him two years to find another alcoholic and for the first group. That was in 1946. He only had contact with AA new York by snail mail. Reading the foreword to the second edition gives a good idea of how well AA was working by 1955.
Through those years, 1935 to about 1955 the groups tried all sorts of other activities involving non alcoholics of various kinds. In every case they failed hence tradition 5 about singleness of purpose, which came about through experience.
Loss of control and choice are the defining characteristics of the AA alcoholic. I had lost both long before I became too sick to continue.
Yet I had buddies who were hard drinkers, knocking back a steady quantity most nights of the week, like four to six nights a week. Very bad for their health, a definite problem, but they never lost control nor the power of choice. They did not have the behavioural or emotional problems I had. Their lives were steady, for want of a better word. One or two stopped on a doctors warning. I wanted to be like them but lacked the control. I am glad I didn't get my wish as practically all of them died in their fifties.
These guys were problem drinkers for a different reason. Straight out health reasons. That is why alcohol would be banned if it was discovered today. In drug terms it belongs in the same class as heroin. As a carcinogenic, it is in the same class as cigarettes. It is a cause of heart disease, liver disease, a whole range of cancers. Even alcoholism didn't exist, alcohol is still a threat to health.
The AA program has of course been developed and changed to treat a variety of conditions. I am told there are something like two hundred different fellowships out there developed for all kinds of problems. The AA program has always been freely available to anyone who wants to develop a spiritual way of living, and to people with other afflictions who want to utilise the program in a fellowship of their own.