You have to compare 'like' things where weight is the only difference.
Discs - take discs of the same mold but different weights. They are the same. Same shape, etc.
Balls - a whiffle ball is plastic with holes and a baseball is rubber or cork center wrapped in yarn and covered with white horsehide or cowhide. Now, change the inner material (rubber/cork) to something that reduces the weight. Now you have a true comparison.
Well if you take a solid plastic ball (I have a few the size and weight of a baseball) and then one of those plastic air filled playpen balls for kids, the solid plastic ball goes easily 2-3 times as far if not further, depending on who's throwing it. The point still stands I just wasn't as specific as maybe some of y'all's taste would prefer hahaha
Discs are only dealing with 10-15% difference in weight. It's easier to determine the difference when it's more like 2-300%, that's why I was using such an extreme example.