Tableau is great, but it has a much narrower use case: given one or more tables of data, generate graphs for presentation or for exploring the dataset.

In comparison, Excel can do that too (just worse), but it can also solve equations, do your company's bookkeeping, and pretty much every other task that relies mostly on numbers.

I would argue Open/LibreOffice Calc comes fairly close to Excel if you ignore the worse user interface (which is fair in the original assertion that it's "mostly polish and small incremental improvements")