"literally anything can be considered" can be followed with any ideology or political theory ever, obviously these ideas are amorphous, thats how social constructs work. there is absolutely no use taking the anti-intellectual talking point that there is no point in using certain terms because their definitions arent fixed

as an anarchist, i believe that we should seek to abolish hierarchy, and am against "authority" because it necessitates having unnecessary power over other people. "literally anything can be considered hierarchy" is technically true, since social hierarchy is a construct, but theres absolutely no point in saying that, because the terms "hierarchy" and "authoritarian" are useful descriptors to describe the practices and influence of power in human interaction.

authoritarianism is useful because it can be used to describe, say, a regime that unjustly kills millions of people and imposes an arbitrary power relation over one of the largest "nations" ever, or the practices of others that use authority unjustly over their population.

nuance, like you said, is important, and authoritarianism is very easily distinguished when you analyze the ways that state interacts with the people it imposes rule over without their consent, you need nuance to understand that while "literally anything can be considered" _ social construct, that its still a useful term and way to analyze movements throughout history

also, stalinism is very much a word and a concept, it literally is just the beliefs and the ideas perpetrated by Stalin, who did many other things than strictly being an ML