> there are a dozen people or so that could destroy the whole system if they so chose to. Overtly or covertly

How so? According to https://www.blockchain.com/charts/pools, it would be no easy feat to start controlling more than half of the current network. Even if some of the pools got together. And if you launch such an attack, it would be easy to notice what's going on.

But if you do have some idea on how the network could be overtaken by a "dozen people or so", please do tell as you have some unique insight.