> Maduro wasn't the leader of a country

Maduro was the leader of the country. Leadership is a practical matter, it doesn't depend on elections or democracy. Stalin wasn't elected either, and nobody says "he wasn't the leader of the USSR".

Likewise, there are leaders of countries who weren't elected that are currently aligned with the US, and nobody claims those leaders aren't the leaders.

A dictator or a king aren't elected, but sometimes they are leaders nonetheless. They are leaders if they de facto lead their countries/kingdoms. If insurgents wrestle control, they cease being leaders.