I like your post, if for no other reason than the fact that you are one of the few people who throws around the term "evolution" and actually understand what biologists mean.

That said, I agree that few small pieces of software "evolve" in any meaningful way. However large ones often do, for exactly the reasons that you describe near the end. As an example, read this description by Linus Torvalds of what Linux development looks like.

And a design note. A large fraction of people's misunderstandings about evolution come down to their trying to say that evolution should be good or right. It isn't. It is about what actually happens and is effective. It doesn't matter whether we want to see evolution happen, evolution is what is going to happen, ideas that can reproduce themselves will become common. You can argue that it shouldn't, you can fight it, you can cry about it, you can accept it. Doesn't matter. It happens anyways.

For a classic essay on this, read Lisp: Good News, Bad News, How to Win Big, which gave us the phrase, Worse is Bettter. (The words "worse" and "better" come from describing the same thing by two different sets of norms.)