Even in old and established democracies, there's usually a large gap between what is said of the democracy, and what the democracy actually is and does.
> You need a rule of law, to tame corruption and no non-democracy has that.
As far as I can tell, that implies the only combination that's impossible is non-democracy and non-corruption. Ie all non-democracies are corrupt, but some democracies might also be corrupt.
Btw, I don't think that's even true: British ruled Hong Kong had rule of law, but no democracy.
However statistically, there seems to be at least a weak correlation (negative) between corruption and democracy.
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 can and does happen in democracies, too.
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.