How much is a swashplate system more energy efficient than a fixed blade system for the same load
The question does not really make sense: a helicopter is a kind of aircraft, a drone is a mode of how a vehicle is controlled.
I can rip the seats and controls out of a helicopter and put some clever software, some cameras, and some transmitters inside, and boom: I have a drone that can carry exactly as much as it could before – probably even more because humans and safety systems are heavy, and we got rid of both of those.
In fact, that's exactly what some companies are doing. The Northrop-Grumman MQ-8C Fire Scout is literally just a Bell 407 with some added electronics and software. And while this particular drone is designed for combat, there are others which are designed for cargo delivery. For example, two uncrewed Kaman K-MAX were deployed to Afghanistan already in 2011.
Here is a video about the Office of Naval Research's Autonomous Aerial Cargo/Utility System AACUS program. The goal of this program is to have a software/hardware package that can be installed in any helicopter to make it fully autonomous. There is no reason you couldn't install it in a Mil Mi-26, for example.
So, in short: by turning an existing helicopter into a drone, a drone can by definition lift just as much as a helicopter. By designing a helicopter specifically as a drone, you could potentially lift even more, because you can get rid of all the weight for the cockpit, seats, life support, safety systems, controls, etc. You could also remove a lot of redundancy, if you consider occasional crashes acceptable when no humans are on board.