> (specifically: it's the vector that rejects pluralism, divides the polity into "the people" and "the elites", and declares that a particular political agenda, in its entirety, represents the true will of the people)

The elites vs the people distinction is usually the key characteristic of populism in most definitions. Populist movements also tend to be very anti-establishment. Many vectors for influencing politics don't involve viewing society as this battle between the people and the elites. For example, while it's true that left-wing populists exist in the US I wouldn't describe the current Democratic party as a populist party. It is more of an institutionalist party and they don't tend to attack elites, because most groups traditionally considered part of the elite support the party. This is in contrast to the current Republican party which very much casts itself as being opposed to the elite. All the rhetoric about battling the deep state and draining the swamp is very much populist.