I would love to. Unfortunately, it looks like the flattening is a deliberate choice they’ve made, as Nicolas informed me:
In that bug report that I submitted, an airport I did had a control tower on a hill overlooking the airport. The hill was intact during my development. After it went into production, the tower was sitting on the ground. No hill. And it looks like this happened by design.
There is an airport I want to do in the World Hub with a famously-sloped runway, but I’m afraid that if I touch the airport, the slope will disappear.