"But I am not convinced of the use case of Powerpoint for the small office"
A "small office" means a lot of different situations - including many that may require the use of Powerpoint - maybe just to open someone else's presentation, or add your contribution to an existing one.
In the years I worked as a contractor, I had often to work on parts of a larger presentation, and when not using my customer's systems, I had obviously to have my own software available.
Don't get me wrong, I don't like how much many people and company rely on Powerpoint to deliver information, but that's what happens, unluckily. And it's even worse when it became used by schools, instead of delivering a properly written text.