You see it as a hindrance, but in fact it is a design feature.
First, all of ZBrush’s strokes are a series of points. Among other things, this allows brush strokes to be recorded and played back.
Beyond that, the fact that cursor speed influences dot spacing gives you yet another level of control in your work. Want a nice, smooth line? Move the cursor more slowly. Want something more randomized? Move the cursor very quickly.
If you want fast movement without the dotting effect, simply turn on Lazy Mouse mode. To see the difference it makes, try drawing a stroke fast enough to get the dotted effect. Then press Ctrl+Z to undo the stroke, turn on Lazy Mouse, and press Stroke>Replay Last. You’ll see a very dramatic difference!
In the end, ZBrush comes down to offering as many options as possible for your work. It operates under the philosophy that it’s better to have more choices for maximum freedom than few choices which can end up restricting you.