I think you may be misunderstanding the point. He mentioned Bitcoin as an example of a sufficiently decentralized network compared to other payment networks. He is correct, though. A decentralized network can never be "lighter" than a centralized infrastructure. Why else do you think the entire internet is built on a simple client-server basis? The concept of decentralized networks wasnt invented yesterday, you know? And you are probably confusing the concepts of a decentralized network with a distributed network, which can be "lighter" with proper load balancing.
Yeah, a decentralized network has to have many working nodes that can be anywhere in the world in order to perform the functions that they are designed to perform but in a distributed network there's a central node that controls the rest of the nodes and that's why it's way energy efficient than a decentralized network.
The main benefit of decentralized network is that if one node somehow fails working then others will do the job without any issues but the problem with such system is the energy consumption as it mainly consumes way more energy than a distributed network. If I'm not wrong then in a distributed network if main node stops working then other notes may not be able to perform its job.