This part:

But there are 55 different options in the data validated list that forms the toggle, each one resulting in 27 lines of data for the flat table. Due to the size of the workbook (amount of data and number of calculations), adjusting the toggle takes the workbook around 45 seconds to calculate.
is not very clear, which is why I suggest you upload an actual sample workbook. To do so, in Windows Explorer, you can right click the workbook and Send To >>> Compressed (zipped) folder, and you will then be able to upload.

If you do that, I'll attempt to help; if you still don't think it's necessary, I'll bow out and let someone else jump in.