They use a hybrid system now and only use peer to peer when dedicated servers aren’t enough, so they could just swap to purely dedicated servers.

However ignoring that, even a peer to peer system can do similar tricks if you don’t isolate the host peer to just one machine. That can even be done by spot checking with a company owned server. You use the server as a verification peer and have it as a backup host to the assigned peer. If your verification peer gets different ram values or what not, you shut the server down at the very least and place that peer on a suspicion list.

But even if they went the cheap route, just distribute the peer network. Let’s say that you have a game of 12 people. You could make it so that each peer is only assigned a certain part of the simulation and players (with overlap on assignments) and cannot track the entire simulation. It’s more complicated than a single server hiding info from you, but they could at least make it to where you’d need multiple infected peers to take over a lobby.