I don’t want to go too far down the rabbit hole to stray from MSFS, so I’ll say what I have to say, and you can have the last word, if you’d like.
Aircraft circle the Earth, but they do not orbit the Earth. In orbit, you are moving tangentially to a gravitational body so quickly that you fall at a rate such that that body’s surface curves underneath you before you hit the ground. Not even the SR-71 Blackbird achieves orbital speed.
While in orbit, forward thrust translates to a higher orbital altitude and possibly a different orbital eccentricity, not forward motion. And, any travel to other celestial bodies would have to take their gravity into account, which is not modeled in the sim.
When it comes to breaking out of Earth’s atmosphere, you would also have to consider your latitude and orbital inclination to determine the extent to which the Earth’s rotation helps or hinders you.
Another thing to consider is acceleration due to gravity, which is is 9.8 m/s² at sea level and 9.7-something m/s² at a jet’s cruising altitude. So I’m sure that that difference is not modeled in the sim, but it would need to be.
The laws of physics are the same everywhere in our universe, but I’m sure there’s a lot that hasn’t been modeled.