and constant follow-ups. The same numbers get calculated,

It’s also likely that the above process
It’s also likely that the above process is stitched together with spreadsheets,
It’s also likely that the above process is stitched together with spreadsheets, internal data dumps, 

is stitched together with spreadsheets, internal data dumps, emails, and constant follow-ups. The same numbers get calculated, rechecked, and entered again just to make the payment, and then the whole exercise repeats itself during filing. It is not the complexity of TDS that drains teams; it is the chaos around it.