First of all Stalinism wasn’t communism. The central idea of communism is collective ownership (the proletariat owns the means of production), and that didn’t happen in Stalin’s Soviet Union, did it? It wasn’t a “bastardization”, if it didn’t have the central feature, it wasn’t communism, period. It would be like a “Christian” who doesn’t believe in Jesus Christ.
The idea that the Soviet Union was “communist” wasn’t just capitalistic propaganda, it was also Stallinist propaganda.
All the models that are called “communist” are in fact Lenninist and do not have the central feature of communism.
As for the “human nature” argument, it is a ridiculous fallacy as you immediately intuited. It is mathematically impossible for 100% of humans to “hoard” power, by definition only a minority can do that, and only a minority does that.
If this “human nature” feature is only exhibited by 1% of the population, that’s not the norm, that’s the exception.
And it ignores all the countless examples we see all over. You can find YouTube videos where humans risks their life to save a stranger’s baby, or even a dog drowning, there is no monetary incentive for these kinds of altruistic behaviors.
Capitalism can’t explain phenomenons like Wikipedia either, where millions of humans altruistically improve the site for no monetary gain whatsoever.
There are many more examples: open source, Linux, Android, Blender, OBS Studio.
This argument ignores the vast majority of people and focuses only on a minority of greedy exceptions.