When David Allen released his book "Getting Things Done" (GTD) over 20 years ago, it was like a revelation. Everyone was into GTD and was creating lists, defining contexts (@errands, @groceries, @phone, etc.) and talking about "Inbox Zero": process everything into meaningful lists, leave no stack (email-inbox or desktop) unprocessed.
David Allen was fully into lists, and he recommended not to use the calendar for task management, only for appointments. It was "sacred terrority". Why? Because the calendar can never hold as many items as lists, and he had hundreds of items in those lists. And he started his system from the observation that people manage their lives with their calendards, because they don't have better alternatives.
Fast forward twenty years later: After a detour via Bullet Journals (slow down, create one page for the day, and try to focus only on those items), the calendar and time boxing are all the new rave. Why? Because lists tend to be a magnet for items, and they get more new entries than we can process.
I am predicting the calendar will be out of fashion for task management in a year or so. And then we'll go back to post-its maybe?
The thing is, no system is able to handle the amount of commitments we have in modern day life, either internal (I'd like to lose weight, be a good father, community member, have control over my personal finances, be a good spouse, etc.) or external.
Observing people who are highly productive, I realize they don't even have a task management app or a proper calendar. They use whatever they have (a piece of paper, Notes app in iOS, their email inbox (mailing themselves), or whatnot), but they have a sense of urgency, laser-like focus, and ignore most of the demands thrown at them, looking like egoistic psychopaths, but getting big sh*t done, all the while we mere mortals write on HN or curate our (latest) todo lists or calendars.
What to make of it? Productive people use what is available, put more focus on the task at hand instead of the tools, and have a sense of urgency and focus on very few things.