As I understand it, the majority of the hashing power. The trick is that hashing power alone can not dictate the network, else the users disappear and all that hashing power becomes worthless. So we have cryptografically reproduced a problem of governance present since the dawn of time.

It's ruthless because existing nation-state actors or other rich actors could invest in mining hardware to take control of the network.

Existing power structures (wealth & access to GPU) translates to power over BTC.