Aetherflow and Ammo should not be compared. Aetherflow isn't a slight damage augmentation, it allows the limited and restricted use of some very powerful abilities. Ammo just increases your DPS slightly and ensures procs, which are already 50/50. A SCH has to choose between using stacks for instant single target Healing, Shielding the raid, DPS, instant AoE heal. Due to the wide range and potency of Aetherflow abilities, they allow you to stack hold the charges indefinitely. Ammo is less dynamic and has a specific use.