We shouldnt underestimate other system agents, such as witness for example. He is the main agent of creating and verifying the block, and one decides the major policies.
Their main duty is to maintain and grow the platform?
You are right. 20 people are elected through a vote, and 1 person out of 80 reserved witnesses is randomly chosen and participates in block producing. 20 elected witnesses are given the right to elect 11 advertisement nod people.