The drone definitely beats out the exocortex on action economy and damage output, but as a fan of Ender, I just can't resist.
My intent for my exocortex is toughness and unexpected action/abilities. Mine is an android and I intend to pack extra equipment in him and take the shield ability and pack one of those charging upgrades as well. I am considering the makeshift baracade and the overcharge abilities, but the extra drain might not be worth it.
All in all it will be interesting to see how it comes out.
Personally I think moving the multitasking down and having the third tier add an attack would balance out exocortex just right.