The real question is not if a more efficient system is possible.

The real question is:

What is the most secure system possible ?

So far I have seen two systems:

1. Majority of vote. (suggested alternative coin system).
2. Majority of computational power (bitcoin).

Now you have to ask yourself a question which system do I trust more ?

Do I trust in "votes of the people/systems" ?

or

Do I trust in "computational power of the people/systems" ?

Both can probably be "gamed"... so...