Tableau makes most straightforward analyses much simpler than attempting to do it in Ipython/pandas, especially when connecting to standard corporate data warehouses (probably on the order of 10x faster). Of course you quickly hit a ceiling in terms of complexity, but most analysts never really get to that point.
Simple analysis usually answer recurrent questions, for this there is reporting and Tableau is not a good tool for reporting (too slow).
For ad hoc analysis instead, there is really nothing more powerful than R or python and it's plenty of tools & libraries that give you the speed you need.
Analysis --> Ipython
No room for Tableau and similar.