Of course we don't. Even if the earth were perfectly flat, currents would cause some unevenness in the sediment deposit.
The sediment wouldn't have been deposited like someone frosting a cake. It would settle out and would be thicker in low and valley areas, or under the oceans, than on mountain tops. Be real.
You claim to be scientific and get something so basic wrong, and then wonder why people don't buy the ToE tripe that evolution happened when they can't get something so simple correct.
The "global flood" is supposed to have been about 4350 years ago.
That is a time period that is easily studied by archaeologists and soil scientists.
There is no global silt layer at that time period. Rather, there is continuity of culture and DNA before, during, and after that date in most of the world.
You are following a religious belief, while denying overwhelming scientific evidence to the contrary. You should at least be able to admit that much, rather than trying to bend and distort science until the data "fits" your presuppositions. The latter is not science but apologetics.
You're right! Which is why you're conflicting with the evidence. There's a thicker layer of sediment on the continental plates than on the ocean floor. Oops.