It's nothing to do with peer-to-peer vs client-server. The main issue is keeping the blockchain up to date. Client-server can actually be more efficient than pe

It's nothing to do with peer-to-peer vs client-server. The main issue is keeping the blockchain up to date. Client-server can actually be more efficient than peer-to-peer in disseminating blockchain updates, but it's still not enough. Bear in mind that, in order for all users to keep a full copy of the blockchain, every time a transaction is carried out every single copy of the blockchain needs to be updated. Beyond a certain level that simply isn't scalable, as it has a big impact on performance. The only pragmatic way to scale the network beyond that point is to only have some nodes having a full copy of the blockchain, at which point you've got more of a client-server model.