> If you have half the typing speed, revising takes twice as long
In my experience, this isn't true. When revising, most of my time is spent considering what changes I can make and not putting them into practice. If the bottleneck is thinking, raising your typing speed will provide marginal gains at best.
I'm not suggesting that revising is solely a matter of re-reading and re-typing. I'm suggesting that I've found them to be a notable component, and that I can do more revising when I can quickly take a possible revision and type it out and reread it to see how it looks.
In my experience, this isn't true. When revising, most of my time is spent considering what changes I can make and not putting them into practice. If the bottleneck is thinking, raising your typing speed will provide marginal gains at best.