The best idea would be to do the pivot already in Mendix, but for your use case, mapping of 100’s of columns, there could be another option. You do need the Excel Exporter module for this:
Once the user downloads the Excel file, based on the above configured template, the user needs to trigger the macro with the chosen short key combination.
In this way the data comes from Mendix but the heavy lifting of generating such a large pivot table is still stored in Excel.