GDP per capita in the Soviet Union continued growing until the end with a couple of minor drops - the collapse in Russian GDP per capita first accelerated with the collapse of the Soviet Union.
The 70s and 80s provided slower growth, sure, but still growth. As far as I can tell there was no drastic decline in GDP per capita growth for the Soviet Union until towards the very end of that period, when the rapid changes from Brezhnev to Andropov, to Chernenko, to Gorbachev disrupted the already weak growth.
It's not that I'm suggesting everything will grow the same irrespective of regime or system, but that the correlations are much weaker than most people will assume.
"Disrupted" is a bad word to use here, it's like saying a surgeon "disrupted" a body of a dying patient. Gorbachev had no choice - the Soviet economics was dying. There are many books and doctoral theses written by now about how exactly and why it happened, but what you describe as "slower but still growth" was the process of slow economic collapse. Nothing worked properly by the time he took over, basically. He tried to deliver some CPR and defibrillation by introducing sort of NEP 2.0 (hey, it worked for Lenin!), and "acceleration", and "perestroyka" - but it was way too late. By then, the collapse was inevitable.
And it's not like the top Party functionaries didn't know that - they were aware of it in the early 80s (in 1984 they started introducing kinda sorta markets between state enterprises - see Khozraschyot) and by the late 80s they were in panic - that's why Gorbachev had to "disrupt". Because they had to do something to try and save the collapsing economy. Unfortunately for them it was impossible.
The 70s and 80s provided slower growth, sure, but still growth. As far as I can tell there was no drastic decline in GDP per capita growth for the Soviet Union until towards the very end of that period, when the rapid changes from Brezhnev to Andropov, to Chernenko, to Gorbachev disrupted the already weak growth.
It's not that I'm suggesting everything will grow the same irrespective of regime or system, but that the correlations are much weaker than most people will assume.