Or, as with Hitler, they can take over a formerly-democratic country and plunge them into war.
His scale may identify a certain kind of authoritarian, but his work is almost assuredly blind as a bat to others and not a comprehensive take.
But you're also wrong on two counts:
First, he wrote this and did most of his work at a time when power structures were clearly right wing. But the mechanisms he describes are universal and independent of the labels used by those in power: authoritarians will strongly conform to the dominant ideology, and social dominants will pretend to adhere to it to gain power. He just used the labels reflecting the situation at the time.
Second, he specifically points out that authoritarians in the Soviet Unions were nominally left wing.
Consider that this kind of shift in dominant ideology is a slow process, on a period longer that one academic's career.
I invite everyone to read this, this is the single most important work of political science / social psychology I've ever read.
Two categories he identifies, "authoritarian" and "social dominant" map to Graham's "passively conventional" and "aggressively conventional." The latter also tends to correspond to what psychiatrists would describe as narcissist, anti-social and possibly psychopathic traits.
For example, he conducted experiments as role playing games, like a model United Nations. When he removed the few "social dominants" from the player pool, the game ran smoothly, there was peace and everyone went to Alpha Centauri or something.
But when he added a few social dominants, things went to hell quick, and nuclear war broke out. Note that social dominants / narcissists are typically at most a few percents of the population.
I'm sure many people have noticed the phenomenon in any organisation: when a narcissist gets a modicum of power, they can destroy an organisation from within.