The horseshoe theory is bullshit not because tankies and nazis don't behave similarly, but because they're not the two logical extremes of the same spectrum. You can be far left without being a tankie by just not being a bootlicker, and you can be far right without being a nazi by (you guessed it) also not being a bootlicker. Even with how many boots you lick the left/right division of the political spectrum is still horribly reductive, but it's super important to split the axis of authoritarianism vs liberalism out of it when addressing tankies, because they have a lot of colloquially left beliefs with the authoritarianism and anti-progressivism commonly associated with the right wing.