I'm not familiar with Four Brothers, but Outland and Star Wars are not Westerns. There may be thematic echoes or homages, but the definition of Western includes a certain spectrum of time and place.
Would your definition exclude The Proposition
and Quigley Down Under
, then, since they're set in the Australian outback?
Star Wars is also an homage to The Seven Samurai, but that doesn't make it Japanese. Similarly, Firefly, which is called a "sci-fi Western," isn't a Western at all; it just borrows themes and imagery from that genre to inform its own identity.
An approach to genre that doesn't take usage into account and totally disregards iconography as a generic marker doesn't strike me as very useful.