No Windows, no Excel license, hundreds of concurrent users. How confident are you that each user is getting the calculations that they triggered and not someone else's? How are you deploying that spreadsheet? How are you version controlling the mutable parts of the system? How confident are you that the solution would be robust in the face of bad inputs and high load?

I won't say there wasn't risk, but there was quite a bit of testing and a human always made the final call anyway (I never fully understood why we didn't eliminate humans from the processes altogether).