You missed the point. If mutations occur because of a particular tendency to mutate, then a species will develop traits that are harmful in all environments.
You appear to be hooked on the "all evolution must be good" kool-aide.
There is no evidence that mutations survive because they are beneficial, there is only the fact that mutations survive because they aren't bad enough to terminate the species.
You should question more of what you have accepted as fact.
I return to the giraffe. There are no short species of giraffe, despite an abundance of ground level food that has kept numerous other competing species around during the same period of time that the giraffe mutated. There are tons of negatives to the giraffe's structure. So why would we think it evolved in order to survive? Far more logical to conclude that it evolved due to a one-way tendency of a given gene to mutate, and the species has survived inspite of the mutation, not because of it.
How is stating that some mutations are harmful a way of saying that all mutations are good?
Of course there is a short species of giraffe. It is not called a giraffe. It is called an Okapi. Both giraffes and Okapis descended from a common ancestor.
A trait that is helpful in one environment may be bad in another. Barriers are very important to understanding evolution, as they permit different living things to interact with their different environment, to change gene frequencies. When barriers change, the opportunities and pressures on species change.
Creationists demand not only special creation of each species but also special delivery to an environment where that species can survive/thrive. By contrast, evolutionist have studied the effect of barriers, or lack of same. Darwin in particular wrote many papers that combined laboratory (or bathtub!!!) study of plant/seed viability, ocean currents as a means of transport, to predict limits of species extent. Then the predicted species extent was compared with traveling botanist’s reports. That combines to a fair approximation of a controlled experiment.