They also mean usurpers in the sense that they did’t come to power through the usual channels.

I mean, it is kinda stretching it matching it up with populism, but the usual channel was through a popular uprising, and it’s why Plato thought democracies necessarily “devolved” into tyrannies. The rabble get a taste, and because they’re ignorant, easily-swayed rabble they support this asshole tyrant’s claim to power. Otherwise, it generally had neither positive or negative connotations, while today it’s universally used negatively.

Can even find a hundred articles making the Plato connection with trump, when we’d mainly just call him a populist.