For totally borking the AI and ability of Siphon Drones and making them near useless now.
Yes, their drain should be able to be resisted, not completely ignored.
I had an entire load out of Drones on a Borg Sphere and it was continuing to fly merrily along without any noticeable effect on it's power.
The Drones AI itself is really wonky. A lot of times I'll send them after a target, only to have them attempt to drain EVERY SINGLE TARGET on the way there, before they finally reach the target and attempt to drain it, but usually end up falling behind if it's a moving target, as they'll approach, attempt to drain while still, instead of say swarming over the target like they used to, and since their drain is not as powerful, they will continue to stop-go after the target, all the while barely draining any power at all.
Seriously, Siphon Drones were the saving grace of bad STF Elite PUGs, as I could shut down the boss/Tac Cube effectively and let them beat on it without any thought. Now I'd be better off not bothering to launch anything rather then Siphon Drones unless the target is completely stationary.
I truly hope they switch the drones back to the previous fire-and-forget AI where you could target one enemy, launch drones, switch targets and know that the target you launched them against was being put to sleep.