Bitcoin's goal is a decentralized democratic value system.
It absolutely is not. A democracy is a system where the majority of participants can decide for everyone.
In Bitcoin, nobody can decide for you. A Bitcoin node will verify all blocks and transactions that others produce. It does not at any point what other participants in the network think or do, if they don't agree with the rules you enforce, they simply don't exist from your point of view. In other words, in Bitcoin, your choice of participation is choosing the rules the system has. If you disagree with those rules, you are effectively on a chain fork - which is essentially its own currency.
There is one exception to this everyone-validates-everything model, and that is double spending. If someone produces two conflicting transactions (which spend the same money) and broadcasts them on the network, the system somehow has to make a determination about which of the two is to be accepted. There is no objective rule that everyone can enforce here. You can state that the first one is to win, but unfortunately due to the finite speed of light, it is impossible for geographically distributed entities to jointly come to the same conclusion about who was first. To solve this problem, miners are introduced. Their only power is cooperating to building up versions of history, resulting in the ability to decide the ordering and timing of otherwise valid transactions, up to and including the power to delay transactions indefinitely.
For miners, hashpower majority matters. But this is not a democracy (it is not one miner one vote, it is one hash one vote), and they do not set the network rules through it. All they can do is either cooperate, or disrupt. The system is designed so that disruption is less profitable than cooperation.
Now, your main concern stands. Centralization of power in mining is a dangerous trend, as it gives small groups of actors a large power to disrupt.