They come to more or less the same conclusions, but for entirely different reasons. The former's argument appeals to the efficiency and productivity perceived to be afforded by a libertarian society. The latter has everything to do with whether or not the existence of, say, public schools is just. Either side will tend to argue that you, luckily, don't have to choose between prosperity and justice, but always fall back to their philosophical roots.
But what if the USSR had managed to keep a high standard of living, comparable to how it did quite well in science? And let's say it also avoided some of the worst bouts of mismanagement, like the large famines. Even libertarians who argue that central planning is inefficient might grant that it's at least hypothetically possible that the USSR could've turned out much better / less badly than it did, had a few things and personnel been different. What would people think of it then?
His guess (iirc) is that, unfortunately from his viewpoint, the USSR is as unpopular as it is basically because it "didn't work": it had a lower standard of living than the capitalist west, large famines, etc. If it were authoritarian but "worked", so East Germans and Muscovites had the same televisions and cars as West Germans and Parisians, he fears the anti-communism consensus would not really be strong at all.
My circuitous point is, the "hardline" libertarian/anti-communist answer to your question is that the USSR was fundamentally incapable of having turned out better. For them, the USSR failing is the same as the experiments that relativity: they are an inescapable result of a fundamental, unchangeable conclusion. You can't just ask "well, what if it had worked" for the same reasons you can't ask "well, what if the experiments disproved relativity?" Experiments can't disprove relativity because it's true, and communism can't work because it's fundamentally ill-founded. To ask what would happen in a world where communism worked is akin to asking what would you drink if hydrogen and oxygen didn't combine to form water.
Please note that I'm playing Devil's Advocate here. I, personally, think that the USSR could have turned out better if it were managed better, although I don't consider myself educated enough on the topic to say how much better. My personal opinions aside, my point is, asking "what if the USSR had worked out better?" is not something you can so easily just ask someone. For some axioms, functional communism is a false statement, and you can't introduce contradictions into an axiomatic system and result in anything coherent. Some people see the USSR failing as an experiment confirming a true statement, not data that serves as evidence for or against a statement.
As far as your hypothetical though, I do think that if the USSR's failing was a contingent, rather than fundamental, result, and if it had not failed or at least turned out less poorly, then that would dampen people's opinions against it. Consider that even with the weight of the evidence against it, there are still people who view it as a nice ideal (with varying opinions of attainability). As the practical evidence gets more ambiguous, that viewpoint looks more reasonable.
Plus, there are plenty of examples of capitalist governments that have had famines and such. India is a notable example.
If the quality of life of the USSR increased, we need to ask two questions. Would it have increased more or less under a more liberal regime? How are you factoring in the murder of tens of millions of people? Even low end figures show that 5% of the peak Soviet population was slaughtered or imprisoned.
Regarding India's woes, systems of government/economy are in no way a panacea. Besides, India's economy was extremely communist, almost explicitly modeled after the USSR. India only turned to liberalizing their markets recently, even later than China.
That experiment is currently being performed in China.
Capitalism is simply a way to harness people's natural selfish motives for the good of society. Neither system is morally superior to the other; it's just that in a state populated by humans, one works a lot better than the other.