Confusion about when it's my navigation, and when it's ATC

Mxsmanic wrote:

Thus, while there may not be much practical reason to simulate the
aircraft at that altitude, since it is physically possible for it to
be at that altitude, it is also possible to simulate it at that
altitude. However, if nobody ever tests the aircraft for real at that
altitude, any simulation of its behavior there remains a matter of
speculation and unverifiable.

Why is the service ceiling of a 172 set so low then? Is it your
contention that if a B-29 dropped a 172 (i.e. "slew") from FL300 it
would continue to fly?

That its engine would somehow magically find enough oxygen to feed the
normally aspirated engine?

You'll construct anything in your mind to maintain your fantasy won't
you?