If the oceans were shallower than today, it wouldn't take near as much water to cover the earth 1 -2 miles deep.
Sudden geologic shifting of mountains rising and oceans dropping.
Through what mechanism?
What is the volume of water required to cover the Earth 2 miles deep?
The amount of “sudden geologic shifting of mountains rising and oceans dropping” would be on a catastrophic scale so great that the extensive fine-grain geologic structures we see everywhere couldn’t exist.
The theory is akin to detonating the world’s nuclear arsenal over England and expecting the result resemble a detailed recreation of Paris.