Cthulhu always swims left isn't an observation that on every single issue society will settle on the left's preferences, but that the general trend is leftward movement. If you interpreted it as that, the fall of the Soviet Union and the move away from planned economies should be a far more important counterexample.

Before continue I should define how I'm using left and right. I think them real in the sense they are the coalitions that tend to form in under current socioeconomic conditions, when due to the adversarial nature of politics, you compress very complicated preferences into as few dimensions (one) as possible. Principle component analysis makes for a nice metaphor on this.

Back to Cthulhu. As someone who's preferences can be described as right wing I would be quite happy with returning to 1950s levels of state intervention, welfare and relative economic equality in exchange for that period's social capital and cultural norms. Controlling for technological progress obviously. Some on the far right of mainstream conservatives might accept the same trade. This isn't to say I would find it a perfect fit, not by long shot, but it would be a net improvement. I believe most Western far right people would accept this trade, most Western far left people would not accept this trade. And in America at least, centrists would be uncomfortable both with that level of state intervention and the social norms of the 1950s.

Now that we have this claim about revealed preferences, let's invoke a very simple heuristic. Imagine you have two players playing a zero sum game of politics, they are offered to move the game to the position it had 50 moves ago. One player accepts, the other refuses. Ceteris paribus which one do you think is winning?