I like your example with the person in front of a crowd. Continuing this analogy - isn't delegated proof of stake, for example, sort of like selecting a guy from the crowd to go and yell the word on behalf to everyone for the next round, after which some other guy is selected? That seems to be both efficient and decentralized. I think your argument does not work against decentralization as such - it shows that some versions of decentralization are less efficient than centralization. Another way how to optimize things is to remove the requirement to have complete consensus with everyone all the time: sidechains and DAG coins do this, in different ways. In short, I believe there is nothing inherently less efficient about decentralized systems, and the current scalability problems are merely technical challenges that the community will solve in 5 years max.

Also, "prorogated" -> "propagated".