The reason a heavier mouse is better than a lighter mouse is the same reason the stick in a fighter plane and the pedals in an F1 car have very little travel but require significant force to move. It’s because your feelings of pressure in your fingers and tension in your muscles are a lot more accurate than proprioception, that is the feeling of your body parts’ positions relative to each other. This means that your body remembers better how hard you’ve pushed something than how far you’ve pushed it. In turn, this improves your muscle memory, your feeling of the mouse, and the connection between your brain and the cursor on screen.
Also, a lighter mouse stops making a difference at some point, for the same reason you can’t throw a ball made of half a sheet of paper any harder than one made out of a whole sheet of paper. After this point, the limit becomes how fast you can move your empty hand. Also, people will look at a mouse that weighs 45 grams compared to one that weighs 50g, and go, well it’s 10% lighter. But your hand weighs a pound and your arm close to ten. So shaving 5g off a mouse is actually shaving some negligible percentage of the total moving weight. At some point, dieting will reduce the moving weight more than a lighter mouse. Shaving 1g makes as much difference as clipping your fingernails.
That being said I’m not the best gamer ever, and I’ve been wrong before!