Your main argument, although extremely well thought out (it is the best one I've seen, and I thought it was interesting so thank you for making it), is based around several statements. There are 4 problems with your points. I will start with the first two. Some things never go away. It will probably be beneficial for a very long time for mountain goats to be good at climbing mountains. The second problem goes hand in hand with the first: if there is no reason for the insects sprayed with DDT to stop being resistant to it then they probably won't since the ones who are resistant will simply continue to pass on the genes. Next I think it is important to mention the fact that the reason why we only have observable modern examples for micro evolution is because macro evolution takes millions of years. Darwin's theories haven't been around that long so we simply haven't been looking for proof. We can, however, see fossil records of trilobites that look distinctly different appear over several million years if you really want an observable example. Finally I don't think you understand just how long of a time roughly 3 billion years is (the estimated time of how long ago the first life forms appeared). This is a really, really, really long time. Over millions of generations of organisms it is completely possible to see such complex genetic code develop. If you don't think so, refer to the first sentence in this paragraph. Seriously. And think of in the beginning when all life consisted of single celled organisms that might reproduce asexually every few hours to days (going off of data from modern day plankton). That's a lot of generations for genetic diversity to occur.