No, I'm saying things I know to be true, because developing 3D multiuser apps in game engines is a large part of my job (and has been since well before AI). I have spent thousands of hours using Unity Netcode, Photon, Mirror and Unreal Networking.

You can throw a couple GameObjects into a scene and synchronize them pretty quickly, but that does not a multiplayer game make. Every single script you write will be more complex when you need to keep multiplayer in mind and testing anything you've written becomes much more involved. This is especially true for a large Open World like Big Walk's.