At a guess I would think you might be suffering massive packet loss? You can run the following, using Powershell, to find out what IP addresses FlightSimulator.exe is currently connected to:
Get-NetTCPConnection -State Established -OwningProcess (Get-Process -Name FlightSimulator).id
You could then try pinging a few of those IP addresses, and see what you get, and whether it widely diverges from what you are seeing in the sim. Some educated guesswork here, and I’m not at my computer to check the syntax, but I believe it to be correct.