Totally agree with your conclusion,
An agile methodology is a tool. The main factor for the success and failure of any project is humans. the responsibility of teams is to adapt the methodology to the context of their project.
I worked for 12 years on Agile Scrum Projects, and each time we tend to a method between agile and waterfall. The most common adaption is to introduce a Project Manager Role, as a separate rôle or as an additional role to the ScrumMaster.