This is why bitcoin is worth so much compared to the other alt coins.
The strength of the network, the pure unfathomable power of all miners together. No big agent can grab 51% of the network, not even a state.
There will be always someone who wants control, and people more in power and authority than other people. That's just how humans work, dominance hierarchies always form.
RE: How decentralized does something have to be, to be truly decentralized?