Yes, this is true in a decentralized and adversarial environment. This is exactly the problem that blockchains have been invented for! In such an environment, w

Yes, this is true in a decentralized and adversarial environment. This is exactly the problem that blockchains have been invented for! In such an environment, we do not have solutions to reach "consensus" apart from blockchains. My point is that apart from cryptocurrencies (where the blockchain is enough because it defines the truth), since you need some form of trusted third-party to make what's written on the blockchain relevant, then you're not in a decentralized and adversarial setting. So you can do things more efficiently, you don't need a blockchain. You don't have to solve the distributed consensus problem.