There is indeed a massive advantage of a mouse over a keyboard-based interface - it's far, far more discoverable for novice or occasional users. In fact, I'd venture to say the mouse (and the corresponding advent of discoverable graphical interfaces) was the primary driver of making computers accessible to non-techies and hence largely responsible for the computing revolution.

But, a keyboard-based interface is still more efficient for someone who can put in the time to learning how to use it efficiently (and customizing it to their specific work), and uses it regularly enough to maintain that knowledge. For a lot of people who write code for a living, a text editor definitely falls in that area.