offline AI provided by the Sim was never a good representation of the real traffic activity at any airport. To get a decent “real world” feeling with offline traffic you need 3rd party AI addons. So far non has been released for MSFS, we at AIG are working on our freeware project but the release will take some time.
For now I would suggest if you want to use offline AI: Set the slider to 100% it wont kill your FPS 