If the whole of England was underwater from rainfall, and the floodwaters all receded at that same time, would it have produced the same result - all of the erosing concentrated in one place?
I am not saying you should be absolutely convinced, but I would like to point out that in the biblical account, the "fountains of the deep" were "broken open" and caused the flood, though it also says it rained for forty days and nights (which would be a possible effect from great catastrophe and geological disturbance).
So while there may be much to criticize in "flood geology" theories, perhaps you should aquaint yourself with what such theories say before criticizing them, rather than the other way around.