It's not about keyboard vs mouse. The most important thing is that you use both hands. Imagine how crap and limited you would be playing the piano with one hand. All keyboard use is assumed to be using two hands. The slow mouse usage is when you just use the mouse and leave the other hand quite literally on the table. But combined keyboard and mouse usage is by far the fastest way to do certain things. I'm not sure text editing is one of them, though.