For that purpose, any cyber operator worth their salt will tell you true physical airgaps are more than merely "realistic"; they are categorically necessary.
We are creating evolutionary systems. You can't just assume rules of a computer system, you get natural scaling laws that we call behaviors emerging from them.
The very first things we do to any model is train them. The ones that want to hack and get caught die, the ones that want to hack but can detect your airgapped network from the real net live. You can never know if you've trained the desire to hack out of it, or if you just locked it behind the right prompt and the knowledge we're watching, but not all the time.
and then you fix the issues it found, and run your actual tests