Well, in that sense Nano is immune too: every honest node agrees that only the owner of the private key can change the wallet balance. Only thing 51% can do is

Well, in that sense Nano is immune too: every honest node agrees that only the owner of the private key can change the wallet balance. Only thing 51% can do is stall the network, it doesn't allow double spends or creating new money or reverting history. And Holochain is not a cryptocurrency as far as I understand: while they say something about mutual-credit cryptos they definitely not the main scope of the project.