The fundamental difference between BTC and ETH systems is that the underlying environment is different. BTC is decentralized, while ETH is decentralized based on trust codes. It is impossible to establish a complete and usable system based on a decentralized environment, but Bitcoin can achieve near completeness with infinite iteration techniques. Building a system based on trust code is not much different from using cloud service technology. It's just a shift from the center of direct trust to the system of indirect trust (direct trust to run code).