The USSR had hardly a non-industrial economy. They actually outproduced the Germans during the war and became the superpower after its end. What you are describing sounds more like WWII China.
Also, it is not true that you do not need industry to fight wars. How are you gonna get weapons and ammunition without it? You either has to produce them or someone has to produce them for you so that you can buy them. Either way, production capability is needed.
It should also be noted that the Chinese had trouble even feeding its own army and it's economy was mostly agricultural. Their offensive capabilities were very small. They had millions of men, but the army was plagued with corruption, poor training and lack of supplies. IRL terrain, poor infrastructure and partisan activity probably saved them.
Also, it is not true that you do not need industry to fight wars. How are you gonna get weapons and ammunition without it? You either has to produce them or someone has to produce them for you so that you can buy them. Either way, production capability is needed.
It should also be noted that the Chinese had trouble even feeding its own army and it's economy was mostly agricultural. Their offensive capabilities were very small. They had millions of men, but the army was plagued with corruption, poor training and lack of supplies. IRL terrain, poor infrastructure and partisan activity probably saved them.