In my project management experience I have taken 2 project management certifications: first level Prince2 and the PMP certification. I also studied some agile methodologies for a while but without finding the motivation to take the certification.
In my experience I have found a decidedly superior completeness in the PMI and Prince2 cascade methodologies compared to the agile methodologies and although neither of them alone can be considered sufficient, the study of both can be considered a wealth of technical knowledge sufficient to face a wide variety of projects.
Prince2 in particular is to be read as a project management methodology in the strict sense, while the Pmbok is a guide to the wealth of managerial knowledge and specific project management skills sufficient to manage projects.
Prince2 has the defect of appearing very rigid as a methodology and almost dogamatic, at least this is the impression that one gets by studying it, in reality to say that you know Prince2 you must also understand the aspects of customization that must be applied to sew the tailor-made methodology of the 'organization.
In general, if they tell you that in a company they tried to implement the Prince2 methodology but they abandoned it because it was too rigid, well, you are entitled to think that in that company we did not know how to customize the methodology to their needs.
As proof of this, the fact that the Prince2 certifications are of two levels: the first level certifies the knowledge of the methodology at the level of putting into practice the techniques described, the second level certifies a level of knowledge such as to be able to implement the methodology in an organization.
The methodology of the Project Management Institute has the advantage of being scalable and adaptable to projects of any size, but it has the 'defect' of being extremely broad from a theoretical point of view and of not providing, within the pmbok, all the tools for its application.
To give an example, while in the Prince2 book there is also an appendix with all the document templates to be used in the various techniques explained in the book, in the Pmbok 4th edition these are missing. It must be said that it is easy to find templates for the PMI methodology on the internet, but once again the feeling is that there are too many and it becomes difficult to make a selection of which ones to use.
The methodologies based on the agile approach, although based on valid principles, the agile manifesto, are still incomplete and inapplicable to projects which by their very nature require a detailed analysis of the final product and its formal approval on paper before proceeding with development. . In the absence of the ability of the agile methodology to manage any type of project, it is natural to think that the cascade methodologies are of a higher level.