And also keep in mind, the "beneficial" mutation step happens in only one animal, that had the mutation when the genes combined to form its genetic expression. And you need several of these steps. It's not like all of a sudden a bunch of proto-birds started to develop wings. Just one animal developed a proto-wing trait, and then reproduced along with 99.99% of others who didn't. But then, the proto-wing happened to be so beneficial despite not conferring an ability to fly, that the proto birds with the proto wings simply died less than the other 99.99%, and started growing in prevalence. And all this still assumes that, at every step from non-wings to wings, the improvements were beneficial for genetic fitness. Now, what if they weren't? How can evolution wait until a string of mutations detrimental to fitness takes place? Wouldn't that make the population with the proto-wings actually shrink -- when it was already 1 animal or so, it might actually be eliminated if we assume proto-wings were genetically disadvantageous before becoming wings?
Again, there is no math in these explanations. Just descriptions and handwaving. Where is the actual math backing these claims and the explanation of the mathematical results! How does it actually work out? It clearly doesn't seem like it should!