That's incorrect. A 51% attack means an adversary having 51% or more of the hashing power (calculated as hashes generated per second) and using it to disrupt th

That's incorrect. A 51% attack means an adversary having 51% or more of the hashing power (calculated as hashes generated per second) and using it to disrupt the normal operation of the blockchain. A party with 51% of hashing power can single handedly create a blockchain that other nodes will accept over any competing chain, meaning they can rewrite history, or prevent any new transactions from being confirmed. If consensus were based on number of nodes, the network could be easily Sybil attacked, given the cost of running what appears to be a node is next to nothing. It would also be difficult to make such a consensus protocol usable, as there's no efficient way to poll a large number of network nodes.