Plato is the inventor of cycles of history and explains political forms as cyclical. Plato conflates economics and form of government as if they were necessarily one and the same. Plato also had a paucity of political forms as well as economic to choose from. In his day there just wasn’t a surfeit of political theory. Actually there still isn’t that much. There are thousands of potential forms of government and of economic organization yet people tend to drop back to the very basic forms that are quite old.
Plato wrote about too must liberty being socially destructive and a protector; a Ceasar or Napoleon, Hitler or Stalin arises in extreme cases, as a protector of a democratic society. The protector becomes a tyrant.
Plato didn’t note that a monarchy is just ossified tyranny with relatives continuing the tyrant’s line and the retainers and bodyguards being the nobility eventually. Fundamentally there are just two kinds of government; those with rule of force and those with rule of reason. Force has tyrants and royals while reason must occur within a democratic society.
Popper was correct about a piecemeal or ad hoc structural approach to government as a democratic society being the preferred form. Plato was correct about realism. Obviously the sub-atomic realm has forms that are Universal at the quantum level and otherwise in steady-state-of-energy-as-mass. Plato was a developer of political theory and did not need to conflate metaphysics with politics.
I should point out that Plato was not so much like Rousseau in his inspiration. Plato or rather Socrates was a supporter of the oligarchy and was a sedulous fellow convicted for corrupting youth in that he tried to get them to revolt against the demos. Plato apparently was an admirer of Sparta and his Republic is a kind of idealized version of Sparta. Plato was a sort of brilliant traitor to Athens and democracy, like Socrates, who mentored Alcibiades- the future Athenian fleet admiral that became a turncoat and led the Spartan fleet.
The trouble with democracy is that it is just and entry level form and philosophical approach. Like an ox-cart, where there is a lot of room for improvement on wheeled transportation and other forms of transportation, democracy needs to be upgraded and evolved into adaptive forms that maximizes efficient human ingenuity, invention and liberty.