Oh, now I understand the problem. You don't understand the difference between a theory of evolution and a theory about evolution. Darwin's natural selection is one of many ideas about how evolution might occur but is by no means the only one nor is it intended to be exclusively correct. Evolution and the process by which is might take place are separate ideas.
The general case in support of evolution derives none of its strength from Darwin's work and would remain exactly as it is if we had never heard of Darwin or if we decisively refuted his theories. Such objections are easy to make, of course, because scientists themselves are always calling attention to certain problems with parts of Darwin's theory, but they do not affect in the slightest the argument for evolution. The theory of evolution was well known long before Darwin. His grandfather wrote a poem about it, and, some forty years before Darwin's book first appeared, Lamarck published a comprehensive theory of evolutionary change. What's significant about Darwin's writing is not the general account of evolution but his description of how evolution might proceed.
To repeat the point: Darwin's theory is an account of how evolution works. If there are problems with that theory or even if it is discredited, that does not disprove the existence of evolution. Just because we have problems agreeing how something works, that does not entitle us to claim that the phenomenon does not exist. If we're not exactly sure how salmon find their way back to their spawning grounds, does that mean they don't go there?
Hence, any appeal to problems with, say, the mutation rate or to the probabilities of random changes producing complex structures or to what is going on at the microscopic level, however pertinent they may be to a discussion of natural selection, are irrelevant to the argument presented for evolution.
