The mathematics of Darwinian evolution is pretty trivial when you look at the individual components. But when you consider superimposing the different processes (competition and adaptation), at first, it is not so obvious how the processes interact. What I think you recognized was that Darwinian cannot be extrapolated to large genetic transformations. It really helps when you can "run the numbers" because something that appears should work, doesn't work when you apply the correct mathematics or run an experiment that demonstrates the process. That's why it is important to correlate one's models with the experimental data.
Another way to look at it, if you live in an environment with disease, starvation, dehydration, predation, toxins, thermal stress,... If the disease doesn't get you, starvation might, or dehydration, or... long before you have a descendant with beneficial mutations to all these stressors.
That's the point. Antibiotics to treat infectious diseases, targeted cancer therapies, herbicides, pesticides, and insecticides are all-important selection pressures that people use in the fields of medicine and agriculture. But we are using these selection pressures on populations that are able to evolve. Understanding how this evolutionary process works is important so that we don't squander these difficult and costly to develop substances.