All the definitions I heard are able to be manipulated easily:
-The/r/bitcoin consensus? Is mainly in existence because of censorship
-User wallets online? Can be easily created with AWS instances
-Bitcoin core? Who decides these bunch of people are in charge to represent all users and not a bunch of other developers?
One obvious alternative is to let Bitcoin follow economic incentives: Bitcoin miners gain Bitcoin, so they have a vested interest that their income is and stays valuable. Thus why not let the miners decide. This is also the only place where you can't influence/manipulate Bitcoin easily.