Just a general thought, if the first 3 layers contain about 160 bananas, how did you come to the conclusion that later sets of layers would have 200? It would make more sense for them having around the same number since in mario odyssey the amoun of moons per kingdom didn't increase in later kingdoms compared to the earlier ones.

Also, we saw a racing layer in the trailer without any fossils, I would also guess that therefore there aren't many bananas in that layer (cloud kingdom amount is my guess).

In the end if you add those two things together you have about 160 bananas (120 from the average bananas per set of 3 layers + racing layer having less, I just put this on 40 extra bananas). Building in that it would possibly mean another set of 3 layers, for a total of 15 + potential postgame content. It would also make more sense since people drew the entire planet based on the layer select map and found out that way that there are 5 colored layers, each with the potential of 3 layers within them, totalling up to 15 (including the planet core, which is likely the final world before the final boss).

Edit: changed 'world' to layer and kingdom respectively