A 20%-30% pressure differential is huge,
The first pound makes such a difference that it seems you’ve got a different object. The next couple of pounds likewise make large, but lesser diffences, and so forth, until it’s at about 7 lbs. from that point the differences become more and more minuscule. After about 10 lbs you are predominantly just compressing the leather and liner. A little more, and only a few people can compress by more than a millimeter if that is all they are doing - which is not what a QB is doing. At 12 PSI, you’re more compressing your fingers than compressing the ball. At 14 PSI, you’re having to do exponentially more extreme things to make a detectable difference...usually requiring things that are not hands.
Try it yourself. The diffences are inversely exponential, not linear.
NBA basketballs, according to USA Basketball, are 29.5 inches in circumference while the WNBA’s basketballs have a maximum circumference of 29 inches. Both should be inflated to between 7.5 and 8.5 pounds per square inch.
Again, Go deflate your tires to 25-26 psi and tell me you can’t notice the difference, let along a guy who’s sold tires for a decade or more not being able to notice immediately a 20-30% psi deficiency. The claim is flat out laughable.