This is a mischaracterization. The bulk of creationist doctrine is modern invention, and in the teachings of the very influential Henry Morris, the Noachic Flood is emphasized as the creative agency responsible for the formation of the earth as geological science finds it.
Creationists are no doubt sincere in their embrace of such teachings as a bulwark to their own Bible based beliefs, but these teachings are not supported by any direct exegesis of the actual description in Genesis I.
You may be right about specific interpretations, such as the idea that the flood shaped the sediment layers and geological formations. That isn’t in the Bible, it’s just a hypothesis.
However, the basics of creationism, that God created man in basically his present form, and created the rest of life on Earth at the same time, shortly after he created the world, is certainly derived directly from Genesis. It’s the most obvious and simplest reading of the text, and one that was the universal Christian interpretation until recently.