Even Etherdelta is not decentralized. There, someone rushes the interface, adds new tokens to the drop-down list, sets the gas price by default. And can turn off all this functionality. You can also turn off facebook, twitter. But bitcoin cannot be turned off. This is what was meant by decentralization.
But if the few big mining companies decide to stop mining BTC, then it's practically turned off. We are still far away from decentralization.