Yes, I agree that GTD isn't a one-size-fits-all solution.
David Allen, in GTD, recommends an alphabetized system. Something that I don't do because all of my reference material is digitized and easily searchable.
Search-ability is the primary reason I avoid keeping a large physical file system.
I take inspiration from multiple books written about productivity and organization. Other books that have been highly influential in my systems are:
- Principles (Dalio)
- The ONE Thing (Keller)
- Organize Tomorrow Today (Selk, Bartow)
- Productivity Planner (more of a journal than a book)