Hey Adam, thx for your question. The problem is when you call both "totalitarian" you are promoting a false symmetry between fascism and communism.
The same things Arendt says about the URSS, like that they were too much "authoritarian", can be said about the so-called democratic countries of the West. Countries, like UK, US, Belgium, France, England, etc., are responsible for many immensely devious episodes of disrespect for Human Rights (until today).
So totalitarianism is a false concept since almost every regime works like Hobbes’s Leviathan. But, communists, however, are responsible for the emancipation of the working people all over the world.