A change will be included with Season 7 that alters the behavior of Siphon Drones. We still consider this a work in progress, and are anxious to hear your feedback on the changes once they land on Tribble (no, we don't yet have a date on that).
The new Siphon Drones will work a bit differently, but are still quite powerful. Keep in mind that the owner of these Drones must sacrifice a good deal of their carrier's potential DPS in order to utilize them, and so they need to remain effective without being as explosively powerful as they currently are. They should be easier to counter, as you'll have more time to react to their effects.
Here's the changes as they are currently checked in:
1) Instead of immediately diminishing the target's power by a large %, the drain of each individual Siphon Drone will slowly ramp up to full capacity.
2) This takes 5 seconds to happen, at which point the Drone will have 1 tick of drain at full capacity, and then shut down for 1.5 seconds before starting again. When the drain turns back on, it is again draining at a low rate and has to ramp back up.
3) This "full capacity" drain is still a % of the player's current power pool. Since the % of drain is low while the player has a large pool, and high while the player has a diminished pool, it causes the overall drain to follow a shallow bell curve in effective drain value, during the first cycle. Subsequent cycles will allow targets to partially regenerate their subsystem power at the edges of that curve, enabling more opportunities to activate abilities that may counter the drains.
4) The amount of benefit this drain receives from the owners' Flow Capacitors skill has been reduced, allowing Power Insulators to be more reliably effective. Although the effects of resisting each tick of a Drone's power drain are hard to see, the "floor" threshold of the overall drain is different for players with a high resistance.
We're still looking into potentially limiting the number of drones that a single carrier can field at any point in time, as well as seeing whether or not it becomes necessary to place a stacking limit (hard cap) on the drain itself (mainly for cases where teams of carriers are using these Drones in tandem). For now, the above changes are all that we've actually performed.
Cryptic - Systems Design