> The implementation of this functionality in a way that will delight customers could hypothetically take 3 weeks as it requires the implementation of an upload button, a datastore to store the uploaded values, and an integration into a legacy feeds system to get the spreadsheet's data to all of the places it needs to go.

> In most scrum processes 3 weeks of effort would not be accepted, and the story would be "broken down" into smaller issues such as "implement an upload button".

You can always find some way to implement something valuable to the user in less than 2 weeks if you actually try. Don't give them an upload button that doesn't go anywhere: give them an end-to-end integration that only works for one of the reports. Give them a network path where they have to save the sheet with a hardcoded filename, if that's still going to save a lot of time compared to manual data entry. Build end-to-end paths that you can widen out, not vertical slices that are useless until you've done all of them.