Meh...
The arc is no less two dimensional than the contrived linear left/right Hegelean model.
True. But I think viewing it as an arc is more realistic than a line, because the more extreme you get, the closer the parties become, both seeking to dominate the populous, requiring a bigger government/military , and totalitarian laws.
It's not realistic because it's two dimensional.
Communism, the far, far, far, far, left: Economic central planning, military dictatorship, a brutal police state, social stratification via political affiliation, propaganda as "news", internment/concentration camps/gulags for political dissenters and other "undesirables".
Fascism, the (allegedly) far, far, far, right: Economic central planning, military dictatorship, a brutal police state, social stratification via political affiliation, propaganda as "news", internment/concentration camps/gulags for political dissenters and other "undesirables".
The trifling differences in the forms of centralized authoritarian collectivist mindsets viz. the dumbed-down left/right crapola is a bunch of academic navel gazing.