I'm not going to dispute that the DOT is a bit hefty, but I currently have my Tempest hi score by using my DOT.
It's probably just an "adaptation" problem -- I'm used to the Tornado with the light touch, and it's hard to teach my muscles that they have to apply a little more "oomph" when using the DOT. That, and adjusting to the slight "play" in the shaft before it hits the outer shaft (and turns the encoder wheel).
It does require more effort to turn the DOT, which helps with keeping moves precise but hurts when you've got to change direction quickly and often. I agree that it's better to play Tempest with buttons for the Fire and Super Zap (instead of the up/down motion).
Anyway, it's kind of like changing types of joysticks...I'm sure it takes a few games to get used to the different "feel"...
Kevin