Last month’s daily bonuses update for Pokemon GO increased the amount of Prestige a rival Gym lost when you defeated a regular Gym member, while the amount of Prestige gained by training at a friendly Gym was lowered. However, developer Niantic has confirmed that the amount of Prestige gained when training at friendly Gyms has been reverted back to the original values.
Pokemon GO amount of Prestige reverted back to original values
Pokémon Blog 