As someone who is not versed in real estate, I don't see why your comment and parent couldn't both be true. Is Dr Horton building homes in Austin? Are the margins in Austin pulling down their average margin? That could explain high profit while dissuading new construction in Austin. *I don't know the answers to either of these questions, but of you do, that could provide some "proof" for either side of the argument, depending on what the answers are.
> Is Dr Horton building homes in Austin?
Yes, a ton.
https://www.drhorton.com/texas/austin
> That could explain high profit while dissuading new construction in Austin.
Given they're still building a ton in Austin, there doesn't seem to be a dissuasion for building there. I do not have any idea about their average margin in the Austin market versus other markets though, but if that was a major decider on whether to build or not the answer is they're still choosing to build.