Fair. But the central idea of scrum is a self-managed team, and there's nothing that says every sprint has to have the same duration, it just makes calculating

Fair. But the central idea of scrum is a self-managed team, and there's nothing that says every sprint has to have the same duration, it just makes calculating the velocity easier. There's also nothing that says you can't pause sprints for some unstructured design and experimentation time, something that I think teams do too little of. The problem is that many organizations don't understand the self-managing aspect and simply put a manager in charge of the team and the scrum, which pretty much sabotages things from the start. This micromanagement, along with imposing unrealistic development timelines, are the two biggest mistakes that I commonly see. Neither of them are unique to agile.