We might think this through....
Say you have an effective flat fast first serve, conti grip.
Isn't it a good serve because the mechanics are good?
Now picture an AmericanTwist serve. If you held the racket exactly the same way, you'd have to LESSEN your pronation to hit the serve, since it's more an upward brush than a flattenning of the racketface to the ball.
Lessening your pronation would mean less efficient?