The thing was, the growth rate from the Tsardom to the USSR was absolutely tremendous...until it wasn't. That growth rate was what made people predict the USSR linearly eclipsing the USA at multiple points in the future, but the anticipated date kept getting pushed back.
Why? Because Tsarist Russia was a backwards totalitarian shithole, and the Socialists directed all government power and seizures to rapidly modernize and industrialize what eas being formerly utterly wasted. Think of it as utilizing a heap of scrap iron and turning it into machinery. Naturally the potential is explosive...but then the USSR ran out of theoretical scrap iron to easily turn into new growth. Their growth plateued. No matter what was tried, Socialism just couldn't solve the incentive and growth issue. Instead, it engendered corruption, stagnation, and ultimately, economic collapse.
Every assumption about the USSR's economic capability was based off an illusion and assumptions rather than the truth of the source of the growth.