Note that Hornet Strike damage is applied before every other damage type. Therefore, every other damage-increasing mod also benefits from Hornet Strike. A weapon with a base damage of 18 equipped with a rank 9 Hornet Strike mod (200%) would have a new base damage of 54: 18 + (18 × 200%) = 54.
This new base damage will be what is used to calculate elemental damages.
Due to how it affects the base damage, this mod is necessary for all secondary weapons in order to use them optimally.