Protocol and client development spans hundreds of contributors and independent researchers. The discussions and development is public; just look at the EIPs, or

Protocol and client development spans hundreds of contributors and independent researchers. The discussions and development is public; just look at the EIPs, or even submit one yourself. Users (non-devs) have agency through the software they choose to run. If mainnet was seriously affected by some attack, users could choose to migrate to a healthier network run by honest nodes. This agency happens with every hard fork: the DAO, but also the PoS merge.