Now you're just hurting your position.
If the world's population was that low
pre-impact not
post-impact, there is an enormous stack of issues with trying to build the infrastructure for an industrialized civilization in the first place.
If this:
Gobeklitepe - The World's First Temple near Sanliurfa, Turkey
Is what you're referring to, claiming that industrial-level technology is necessary to build such a thing or make it stable is patently absurd.
Have you not seen what the Romans built? The Greeks? The Chinese? Are you not aware of how much of what they built is still standing? Do you have no familiarity with late medieval architecture, much less age of sail?
You really aren't helping your position, and if you want to argue this further, it should go onto a new thread.