At long distances it indeed is and I doubt anyone uses WASD for that. However when you need to scroll just a little bit, say half of a screen, then I find it to work better than a mouse. Nothing really prevents you from using other hotkeys, you don't need to have your fingers glued to WASD all the time.
You are missing "return" after the entire "^!z::" block. If you are willing to spend a bit more time on this then you could try to find the big 15+ page autohotkey thread at GR.org which contained a few different WASD camera movement scripts, complete with a working chat (your script requires suspending it every time).