Now...I would definitely expect under inflation to benefit the receiver somewhat but how much of an advantage would that be if the ball is delivered off target because the QB is not used to using a ball in that state?
Does an under inflated ball behave differently? No one except a Pro QB can say for sure. I have played organized football and even played QB for a time. I only base my guesses on experience in handling a football. I'll wait for the investigation to complete before passing any judgement.
What if the cheater practiced with the deflated ball all week and the visitor was unaware the ball wasn’t the same as he was used to?