I think the arguments are stronger against Word than they are for Excel, but they're similar.
If you want to run some simple calculations on numbers, Excel is vastly overpowered and baroque. New version? Hope you've learned the new magic series of GUI clicks. Just like Word, Excel files are not inspectable (again, more baroque 'magic').
I can easily run calculations on plain texts tables in Emacs (along with the normal conveniences of being able to reorder by row, column; apply formulae across a range of cells etc.). And that's all displayed in plain text. And I can easily add new functions, keybindings, whatever, to suit my needs.
But the fact that you say the arguments against Word "can indeed be just as easily dismissed" makes it unlikely that this is likely to be a productive dialogue.
For Word, it's way more complicated than most people need, and again, users are at the (non-existing) mercy of the application. It's not very user-configurable - you have to learn how Word expects you to do things. Again, its data files are non-inspectable monstrosities, with minor corruption causing complete corruption, and fragility between versions.
I manipulate text for a living. For simpler things, it's much easier and productive to use something like Markdown or (for more complex things) something like Org-mode. For complex things, I need LaTeX - Word simply lacks necessary functionality.