The following video demonstrates just how badly server spawned and owned vehicles can affect your client.
I have spawned on server maybe 15 "B_MBT_01_cannon_F" tanks before FPS on my client dropped to almost 10. Server stayed at 49. As you can see on the video I then transferred ownership of all tanks to my client with setOwner command, which almost tripled my client FPS to about 30. At the same time server FPS dropped to 36. I then deleted all tanks but it did not make much difference. It did also improve FPS little bit in my earlier experiments. When I had my server recovered in this video, FPS on client increased to 40.
So this is what I find very strange. Why server owned vehicles lag my client so badly? Why when I transfer them to my client they start lagging server instead? Considering a vehicle usually belongs to the server until someone jumps in driver seat, are you really surprised Arma 3 performs so badly online?
I have already made tonnes more tickets about vehicles and locality in MP problems. Now BIS dudes at least you know where to start looking :)
PS What I cannot test by myself is what if I get ownership of all vehicles will it lag another client along with the server?