Productivity systems work best when they are simple.
Complexity adds complexity, which means that there are more parts and dependencies to manage.
However, simple for the sake of simple doesn’t always work. Too simple is just as ineffective as too complex.
A good system has to be effective, which means as complicated as necessary to actually do the job.
A notebook and a pen might work well as a way to keep track of your task list and schedule, or it might not. It really depends on how much you want to keep track of, how many inputs or people need to interact with you on your schedule…
Your productivity system needs to be as complex as your life.
Of course, complex doesn’t mean the same thing as rich, or deep, or fulfilling.