Behavior: Myself, Parents' Choice

Isn't All Formula the Same Except for $$ ? Baby Wish Tummy Issues Plz Help!

Ok, I'm trying to help my little nephew out! He's formula fed and my sister has been using walmart's parents choice *sensitivity* her son seems uncomfortable, always hungry, I guess the term is gassy or fussy. She has now tried soy based off my mothers suggestion. She went switched to soy before trying any other brands of milk based formula because she was under the impression that all formula must have the same ingrediants. Therefore the only difference would be the brand name. Is this not true? Could enfamil *sensitivity* work better...