Can you elaborate? To me this makes no sense whatsoever, and I can easily provide a counter example. Islam is not democratic in the Western sense, yet its laws curb corruption.
Democracy leads to better government in general, which leads to reduced corruption. People in Islamic countries accurately think their countries are corrupt: https://www.transparency.org/en/cpi/2022
Correlation vs causation. Those Islamic countries are still facing occupation especially from post WWI mandates like Sykes Picot and Balfour, and we see first hand the interest of "democratic" countries to keep things that way to ensure their superiority by force. They are not letting things take their natural course.
What definitions of democracy, rule of law and corruption are you using here?
As long as contracts are being upheld, and court decisions are speedy and predictable, and public officials don't enrich themselves, that counts as low / no corruption, doesn't it?
Democracy might help with that ideal, but it's by no means strictly necessary.
As far as I can tell, an absolute monarchy that is run for the benefit of the ruler can still have rule of law and low corruption.
As an alternate history example, take Lee Kuan Yew's Singapore, but make him king and increase his salary to 1 billion SGD per year (instead of 1 million SGD per year). Change nothing else.
They would still be one of the least corrupt countries on earth, and have a judiciary that enforces the rule of law.
> Rule of law in a non-democratic polity inherently benefits its rulers more than other citizens.
That's no different than if the president of the US used his power to acquire money. The only difference is that in Singapore the law itself has been corrupted to allow it.
Corruption, and even corrupt laws, exist in democracies too, but in a non-democracy all laws are inherently corrupt. Non-democracies have no legitimate basis for even having laws.