Ignoring the health concerns, which can be addressed with a vertical mouse, I don't think mice are necessarily slow. When navigating interfaces that are optimized for visual search, translating the area that I'm looking at into a series of keys requires more cognitive effort than just clicking it. When visually scanning, my I subconsciously move my cursor to the area that I'm looking at.

Whether you want to use a mouse or a keyboard depends on the task you want to perform and its temporal proximity to other tasks. For example, when reading code, you tend to use a mouse wheel and visually scan and select references. A mouse would likely be faster. When typing, however, your hands are already on the keyboard, so VimMotion is faster. Finally, I love hybrid operations such as initiating a screenshot using the keyboard and selecting the region with the mouse.

Whether interfaces should be designed for keyboards or mice also depends on factors such as discoverability, frequency of use, and the amount of available operations. Command palettes are amazing, but they are less discoverable and restricted in their layout. Interestingly, Raycast, the discoverable keyboard-centric app, has a mouse-centric settings interface.

Of course, most of us already intuitively know this, but it's tempting to drink the keyboard cool-aid. I had a phase where I aggressively prioritized the keyboard and was frustrated by MacOS's lackluster support for it. My biggest annoyance with the mouse was the distance my hands had to travel when switching from the keyboard. Removing the numpad helped with this.