Data, logic and presentation sounds a lot like model controller and view. I feel like you suggested most logic should be in how days is handled? But let's be serious here, there's no right way to make a web app. There are certainly wrong ways and inefficient ways. If we focus all our efforts on doing things perfectly well then we would miss the point. Essentially, you're just theory crafting how people should code while ignoring the practical issues of people and coding.