Regarding the talk about wealth being power. Well, no. Power is power. Wealth isn't.
The Soviet Union had enough power to compete with the US for decades. Considering the odds against them I think they did fairly well.
Even the Breznev stagnation is a misnomer IMHO. In the 1970s the Western countries economies were also stagnating and in the Breznev era the Soviet industry managed to do many important military achievements like the Tu-160. Living standards were also at their peak.
I think the main issues the Soviets had was they did not invest enough in the semiconductor and robotics sectors. This caused them many issues from lower productivity because of less advanced machine tools, to worse quality because of high reliance on manual production, to worse oil field prospection and extraction technology. Texas Instruments, for example, started making chips for the oil industry in the US to scan for oil fields. So in the mid 1980s the Soviets started sliding backwards economically.
If wealth was power the Song Dinasty wouldn't have lost to the Mongols. Wealth isn't power. Power is power. But of course, to feed an advanced army you need an advanced industry in the right sectors. Otherwise you either need to confiscate wealth using your military or your military power will degrade. Which is what happened to the Mongols eventually.