I don't think the author is advocating for that type of economy or aiming to show how what every era of communist life. The author used the 1950s and '60s, when the Soviet economy was supposedly at its peak and looked like it would overtake the US, to show how the system was supposed to work in an industrial economy that had recovered somewhat from WW2. The Soviet system was a horrendous failure, I'm not apologizing for it either.
The decline in living standards during the '90s was influenced by several factors, its partly a case of correlation being conflated with causation. Stagnation in the '70s had turned into a decline by the 1980s for economies like Poland and Romania. In a counterfactual where the command economy remained in place and pre-1989 trends continued, the same decline could have been the same or worse than OTL.
The post-communist performance of an economy was generally based on how aggressively the country reformed and how long communist rule had been in place. Poland went through a short, sharp recession during its economic reforms and came out ahead of more gradual reformers like Romania, Albania, and Ukraine. The USSR was at a disadvantage relative to the Warsaw Pact states because 70 years of communism left Russian society without recent living memory of what a functioning market economy and non-communist political system was supposed to look like.
Preconditions to a successful capitalist country like the rule of law weren't in place to make the transition go well in Russia. State assets went into the hands of the bureaucrats with access to them, and normal people who were given vouchers for state assets didn't know what to do with them, there are stories of people using them as wallpaper.