I just don't really see the big deal in the difference. Especially because a dotp exists with the goal of creating the conditions for the stages of communism so why is it separate from the stages of communism? Marx wasn't very clear even in Gothacritik about exactly how the lower stages would look, just that they'd "bear the birthmarks of capitalism", "have distribution of resources according to labor value". Also he frequently mentions the importance of an ever expanding democracy, which is primarily the introduction of democracy in production and formation of worker councils.

Again, it feels like this difference is really splitting hairs as the end goal of both interpretations is the same. Hell, even the intermediate goals and initial goals are the same, they just have different terminology being used.

"State capitalism" is just the highest stage of capitalism and is a vector by which Marx saw a transition to socialism happen in the industrialized nations. Lenin skipped that step with the use of peasant coalitions (which Marx pointed out as a viable option in The Civil War in France). The issue being that productive forces didn't exist in sufficient quantity in Russia to implement the lower or higher stages of communism.

So you could say that the industrialization period and NEP/5 Year Plans were not socialism and in fact "state capitalism", but they were in service of developing industry without the massive human cost of capitalist industrialization (which was a success). So whatever they were, they differed from capitalist production in social equity and human cost. They were an example of a just expansion of production that didn't require reserve labor and wage slavery. Calling that "capitalism" would be wrong, it's an entirely different mode of production.