It might be a delusion in the absence of parallel lines of evidence.
But you are misrepresenting gradualism. Even in geology, gradualism acknowledges the effects of supervolcanos and asteroids -- even planetoids, as with the creation of the moon.
Evolution encompasses many modes and rates. We can observe saltation in plants, as when new species result from polyploidy. We are also learning that some animals have frequent non-fatal chromosome mutations. The more we learn about such phenomena the more obvious it becomes that all the processes needed to account for common descent are happening and can be studied -- eventually in the laboratory.
Variable rates of evolution are mostly the result of geologic events resulting in mass extinctions. Darwin explicitly considered this possibility and rejected it. He was wrong in rejecting it, but he had limited information about geologic processes, and limited information about the underlying processes of variation.
When you imply, however, that saltation is gradualism you are most certainly misrepresenting it.