No-one can claim the attempts at communist states in the past were “not true communism” as an explanation for why they failed, because all polticial and economic systems are subject to the whims of human nature

That's just a bullshit cop out. By the same logic, we can't call any government anything at all, including capitalist, democratic, fascist, socialist, anarchist or otherwise, because they are "all subject to the whims of human nature". That's just sophist bullshit used in place of an argument. Human nature is, and has always been, a cop out excuse to explain away all sorts of issues people don't want to deal with. Why did he kill that guy? Human nature. Why did the Nazis gain control? Human nature. Why is our democracy running contrary to our desires? Human nature.

If they tried to be communist, and failed because of human nature, then it means their system was not capable of handling and taming human nature, and thus itself is the failure.

It's weird that, in the wake of natural disasters, where all state and private factors are cut off, when all the chips are truly down and people are left on their own, we see people helping each other survive, and that isn't considered human nature. No, siree. Thomas Hobbes said humans are vicious animals, so it must be true, and thus it follows we must be "tamed".

No, the USSR wasn't communist because it didn't meet any of the criteria. It was Marxist-Leninist. Socialist. It morphed into a state capitalism, and by the time of Stalin, had become a near-dictatorship.

Its failure, in my opinion, was a massive over-reliance on the state, and severe centralisation of power. Some argue that this is due to its need to compete on the global stage, as a lone socialist power in a sea of capitalist nations engaged in global trade, and cut off from that sea by sanctions and embargoes forced by the US.