Incorrect. Adding bulk will alter your range of motion, it's simple physics. With more bulk in your arms, moving your arms to the same spot is pretty much impossible. You have to adjust shoulder joint movements, adjust release points, adjust hand positions... all of which are critical to shooting. His mechanics are different this year because his body is different this year.
Come on man, you make it sound like he went from a twig to a body builder. How much bulk can you safely gain before you have to change your hand position?