Wolfgang Schwanke schrieb:

It doesn't behave there at all, because it can't get there on its own.
If MSFS allows you to fly a C172 to that altitude, it models it wrongly.

Actually, you're wrong in two ways:

You can get up there in a 172. You just can't go up there on your own
(which you stated correctly). Once at altitude, release from whatever
took you there and look how the3 172 behaves.

Second, todays numeric models are astonishingly accurate. Feed the data
in a suitable program and look how the 172 would behave.

Stefan