Wouldn’t the political spectrum be an utter lack of government on one end and tyranny on the other? That being the case, communism, fascism, Naziism, etc. would all be closely related on the totalitarianism side of the spectrum, rather than opposing ends of the spectrum.

The ancient attempt of a 1d embedding of political ideologies is doomed to fail, however anyone tries. It started out in revolutionary France in 1789 to distinguish between the supporters of the king (conservatives, on the right) and supporters of the revolution (revolutionaries, on the left). It was good enough for that, but it's not for very much else.

The most sensible minimal extension (to 2d) that I know of is to distinguish between how much you value personal freedom on one axis and economic freedom on the other. That still leaves out a lot, but is the best indicator of which side you'll likely to end up on regarding most political contentions, given the simplicity of the model.

There are actually two popular models of that kind, the Nolan Chart (example quiz [1], your spectrum is the vertical axis) and the Political Compass (example quiz [2], your spectrum is the secondary diagonal).

[1] https://www.theadvocates.org/quiz/

[2] https://www.politicalcompass.org/

Such a spectrum would not be particularly useful for describing the behavior of politicians or voters. Consider that someone who usually votes for a democratic socialist party might sometimes swing further left and vote for a communist party, or further right and vote for a liberal party. But they're unlikely to vote for a fascist party. This fact is captured by a left-right spectrum, but not by the spectrum you're proposing, which would suggest equal likelihood of such a voter supporting a communist or fascist party.

Well, every model will have some weaknesses and I suppose it depends on what you want to know which one would be better. I know if I had to choose on the basis of one spectrum with whom I'd like to live in the same country, I'd strongly prefer gp's over the conventional one.

Also, btw, the fascist movement recruited much of it's ideological and political concepts and initial core activist base from syndicalist/corporatist socialist circles and was strongly anti-capitalist/pro-socialist and anti-conservative. Benito Mussolini was for a time chief editor of the Italian Socialist Party's newspaper "Avanti!" and member of the party's National Directorate.