All I know for sure if that people have been calling Shanahan offense, a west coast offense for a very long time now. Who knows... maybe the people are wrong?
These coaches in turn have their own disciples who have used Walsh's West Coast system, such as former Washington Redskins head coach Mike Shanahan and former Houston Texans head coach Gary Kubiak. Mike Shanahan was an offensive coordinator under George Seifert and went on to win Super Bowl XXXII and Super Bowl XXXIII during his time as head coach of the Denver Broncos. Kubiak was first a quarterback coach with the 49ers, then offensive coordinator for Shanahan with the Broncos. In 2015, he became head coach and led Denver to victory in Super Bowl 50.