I think PowerBI compares with Tableau quite favorably. For the most part PowerBI is a clone of Tableau, but it goes farther and adds in much more powerful scripting(M, Python, R), a library of custom visuals, Power Query which is a nice GUI for data transformation, and deep formula language (DAX). I think it's easy for an Excel or Tableau user to pick up in a day, but it scales much more as you have more data analysis expertise.
Also MS has been improving it like crazy over the past few years. They clearly want to maintain their dominance in the data analysis space, but see the winds shifting away from Excel and are not waiting to become irrelevant.
The model isn't that a business user would use Python or R. Rather, a data scientist shares live-computed analytics to business users through a report / dashboard.
Also MS has been improving it like crazy over the past few years. They clearly want to maintain their dominance in the data analysis space, but see the winds shifting away from Excel and are not waiting to become irrelevant.