being able to move the cover around with fingers as if there is an air bubble, or the cover was too big or not properly stitched is another. How the ball reacts to the bat in that situation would be wildly inconsistent hitter to hitter, not just a % of performance overall.
there are essentially 3 or 4 places on earth that make softballs. Doing 100% in the US could cost too much. Quality control on these balls would make them cost too much too. Hence the manufacturing tolerances are allowed to specs. Otherwise you'd be paying double for triple for softballs than now. Bad vs good batches in cores are 100% a real thing. Its not going away.