Do heaver Pokemon card packs have better cards?

No, the weight of a Pokémon card pack does not indicate whether it contains better cards. The distribution of cards in each pack is randomized from a set pool of possible cards, which include common, uncommon, rare, and holofoil cards. The weight of a pack may vary due to slight packaging differences or manufacturing variances, but this has no correlation with the quality or value of the cards it contains. It is the randomness that keeps packs exciting.