You are discriminating land use based on political distinction. If we want to talk about reservoir, technically a bunch o f those housing developments, schools, the West Houston Airport, etc, etc, etc, should all be included. This is why so much of the area was damaged/destroyed by Hurricane Harvey because there aren't significant differences in elevation across Houston basically anywhere.

This issue was addressed years ago. The practice in this area is to carve things out of the 'basin' once the area is developed. You're adjusting maps based on political boundaries, not on reality.

Most of Houston consists of floodplain zones. This was already discussed years ago. The recent change is due to a different editor, who doesn't live in this region, and who doesn't predominately edit this region, just mapping based on political boundaries, just as you are doing now.