Why is it hard to attack?

1, balanced weigths make it harder
for balanced weights, some bits can be random when some can be used to decide the output, so it's pretty hard to determine which part is random and which part contributes.

2, non-linear makes it hard to find centroid (peak delay value challenge).
non-linear erases the quantity of delay difference, make it harder to determine how close this challenge is to the peak delay value challenge.