I mostly agree with this perspective. Alternative agile methodologies may fit better with certain teams (e.g. Kanban, lean, etc) and so having a top down prescriptive method of "agile" doesn't make sense. Another perspective is that Scrum is agile training wheels. Once a team can discipline themselves enough to follow a Scrum workflow successfully for a significant period of time, it shows they are ready to follow a more flexible agile approach and therefore may no longer need a Scrum leader guiding the team.