I suppose thats debatable. There's probably some use for both. A textbook can also be a syllabus and plan for a semester. IE, perhaps a textbook is divided into

I suppose thats debatable. There's probably some use for both. A textbook can also be a syllabus and plan for a semester. IE, perhaps a textbook is divided into 15 chapters, each representing one week of work and exercises. Lectures, tutorials and such can be structured around that. In other cases the teacher already has a structure in mind and they are looking for materials to support it. Both cases exist. I suppose the ideal would be layered and modular so materials that can be snapped together like lego. But realistically, modular is a thing difficult to get right.