I’ve always thought that as well, but for different reasons.
I assumed that the ‘mile thick’ ice sheet that covered North America melted in places forming huge lakes that suddenly merged and burst through in a glacial torrent that carved out the sandstone.....................
From what I have read, the theory is that there was a massive lake, referred to as “grand lake“ that was formed as a result of the great flood, which eventually washed out one of its natural dams and flooded downhill, creating the Grand Canyon. There’s some good resource material to support the theory.