Really appreciate the responses.
Don't know if my house was built in the dry season, its a big builder, 1000s of homes near Bangkok. They are building all year round. Expect that they are cutting corners, the subs are a mixed bag. Concerning (and expected) is all the construction debris left about 20CM under the dirt, I have found bottles, pipes, chunks of concrete, cans, etc.
My gut feeling was that we needed to fill in that space under the house with rocks and give it time to settle.. now I see, that could take a few years of filling and settling. This makes the most sense... maybe after a few years, then we could look at landscaping around the small bit of land around our house.